Seed Germination Theory and Practice
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993 SEED GERMINATION THEORY AND PRACTICE SECOND EDITION Norman C. Deno, Professor Emeritus of Chemistry Published June 1, 1993 (Second Printing November 1, 1993) Based on Experiments on 145 Families, 805 Genera, and about 2500 Species Every species has some mechanism for delaying germination until after the seed has been dispersed. The Science of Seed Germination is the discovery and description of such mechanisms and the development of procedures for removing them so that the seeds can germinate. To Plant a Seed Is a Noble Deed Propagation Is Conservation • •.•• USDA National Agricufturaj Library HAL Builthng 10301 Baltimore Blvd. 8eitsvde. MD 20705.2351 to SEED GERMINATION, THEORY AND PRACTICE Norman C. Deno, Prof. Emeritus of Chemistry, (Pennsylvania State University) Address all inquiries and orders to Norman C. Deno, 139 Lenor Drive, State College PA 16801, USA Table of Contents by Chapters Page 1 (A) Introduction and (B) Principles 1 2 Germination, Definition and Description 7 3 Design of the Experiments 9 4 Rates of Germination. 18 5 Inhibitor Destruction by Dry Storage 21 6 Inhibitor Destruction by Moist Conditions 24 7 Two or More Inhibiting Systems 30 8 Seeds Embedded in Fruits 33 9 Physical Mechanisms for Inhibiting Germination 37 10 Outdoor Exposure and Oscillating Temperatures- 41 11 Photoeffects 43 12 Exogenous Chemical Effects and the Stimulation of 47 Germination by Gibberelins 13 Dry Storage and Longevity of Seeds 53 14 Growing Plants from Seeds 55 15 Collection of Seeds 62 16 Plant Nomenclature 64 17 Endangered Species and Conservation 67 18 Lists of Genera Studied Arranged by Their Plant Families 68 19 Rate Theory In More Detail 75 20 Data On Germination Arranged by Genera 81 21 The Orchids (Orchidaceae) 234 22 The Grasses (Poaceae) 236 23 List of Seed Donors and Other Contributors 237 24 List of References 240 25 Digest of Symbols and Abbreviations 242 .5. DEPT. OF AGRICULTURE )NAL AGRICULTURAL LIBRARY yofl3 RECEIVED - JAN I 51994 ORDER UNIT ACQUISITIONS BRANCH : Zut 31Ji / UTJU3fflaLJM4O1TA1 -. • Cç f WU s:uro - I- FOREWORD TO THE SECOND PRINTING OF THE SECOND EDITION This copy of the second edition of Seed Germination Theory and Practice is from a second printing which accounts for any delays. The experiments on seed germination are continuing and that had to take first priority. As compensation you will get the following brief update on some of the more significant observations made since the first printing in May 1993. Also the opportunity was taken to correct a few errors. The following update briefly summarizes some of the more significant results obtained since the first printing. Alangium platanifolia seeds were washed and cleaned for seven days. Such seeds germinated over several weeks at 70 when treated with GA-3 and not otherwise. This is the first example of seeds in a fruit that had a GA-3 requirement for germination. Adonis vernalis and its geographical variants continue to be a problem. Large amounts of seeds from two commercial houses have proven to be over 99% empty seed coats the same as seed from our own plantings and various other sources. There is need for someone to breed seed viability back into this species. Several more cacti have been found to require GA-3 for germination. It is possible and even likely that the majority of cacti will be found to have this requirement. A definitive article has been written by myself and will appear in the Journal of the Cactus and Succulent Society early in 1994. Caltha palustris required GA-3 for germination. Seeds rapidly die when held moist at 70, and all are dead in one month. This is one of the most rapid death rates yet observed for seeds held moist at 70. Caulophyllum thalictroides and Sanguinaria canadensis self sow on our property yet fail to germinate under all conditions including treatment with GA-3. It is likely that these species have a gibberelin requirement for germination, but that some gibberelin(s) other than GA-3 are required. Note that it was already shown that different gibberelins initiate germination in Shortia galacifolia but in different patterns. The whole problem of gibberelin requirements for germination are obviously complex. It will be some time before they are completely understood. Related to the gibberelin situation is the problem of germination in Trillium. Trillium apetalon and Trillium pusillum have now been shown to require GA-3 for the first step in germination, namely formation of the corm and root. Several other Trillium had this behavior, but others had more complex responses to GA-3. Needliess to say the Trillium problem is under intensive study. Plentiful supplies of seeds of Lysochiton americanum and Symplocarpus foetidus have now been obtained from our own plantings and the proper experiments were conducted. Both were found to require light for germination typical of most swamp plants. Germination occurs in several weeks in light at 70 and none in dark. - Ii - Seeds of four arctic willows (Salix arctica, S. herbaceae, S. lanata, and S; phylicifolia) were collected by D. Haraldsson in Iceland and sent immediately. These germinated in two days at 70. Dry storage for two weeks at 70 completely killed the seed. However, the seeds can be stored moist at 40 for at least four weeks. Such seeds germinate in two days the same as fresh seed when shifted to 70. It is of interest that the seeds turn green when moist at 40, but do not develop further. Sambucus pubens has been found to require GA-3 for germination the same as other Sambucus. This seems to be a general requirement in this genus. Senecio aureus required light for germination. Further, exposure to moist conditions at 70 for just two months led to complete death of the seeds. Vernonia altissima also required light (or GA-3) for germination at 70. It is unusual for such light requirements in species of Asteraceae. I am particularly indebted to Thomas Fischer, Senior Editor of Horticulture, for a charmingly written account of my work. As a result the first printing of the second edition sold out. Purchasers who are receiving the second printing will forgive a somewhat delayed shipment. I also wish to express my appreciation to the many amateur gardeners, seedsmen, and horticulturists who have cooperated by sending me seeds from every corner of the World. Further, it has been the utmost pleasure to see how nurseries and professional propagators have embraced my book with enthusiasm. Many kind letters were received for which I am most grateful. In contrast, there has been little reaction from the academic community despite the fact that my work on seed germination applies techniques more sophisticated and analysis more profound than has been used in past work. There are reasons for this lack of response. The problem faced by departments of horticulture and other biologies is that they can no longer limit-their research to bending over microscopes. To survive they are increasingly becoming pseudo-chemistry departments, because this is the direction that has the potential for large research grants. The previous head of the Department of Horticulture at Penn State had his Ph. D. in chemistry. The Department of Botany, Microbiology, and Zoology are gone. These are the signs of the times and indicative of the directions things are going. The type of work described in this book is not the type that brings in big research money despite its importance to both theory and practice of horticulture. It will be interesting to see whether it ever gets much reaction from the academic community. Finally to end on a note of humility, on recounting the number of species studied, the number is about 2500, not 4000 as given in the first printing. Further, gibberellin and gibberellic acid were mispelled throughout and should have an added letter I. -1- CHAPTER 1. (A) INTRODUCTION AND (B) PRINCIPLES (A) INTRODUCTION The initial concept of this book was to write a list of species with a one line description of the best method for germinating the seed. Such a book would be patterned after the The Seedlist Handbook of Bernard Harkness (ref. 1) and would supplement that book. After reading the six latest books on seed germination (refs. 2- 7), it was evident that the book could not be constructed from data in the literature. The decision was made to embark on a broad program of studying seed germination. At this time the realization came that the germination of seeds is a chemical process, and seed germination should be studied with the same techniques and logic used to study chemical processes. Perhaps these techniques, which had so drastically changed our concepts of chemical processes, would have a similar effect on our concepts of seed germination. Initially the studies were restricted to alpine and rock garden plants, but with each new discovery, the thrill of the hunt increased. Ultimately the studies were broadened to include trees and shrubs and finally tropical plants and the grasses. It became evident that the work was of importance not only to plant growers but also to research, biologists and research chemists. The question arose whether to write separate books for each of these three audiences or to attempt a tour de force putting it all in one book.. The tour de force was chosen, and this has necessitated some words of explanation directed at each of the three audiences. For the plant grower, the directions for optimum germination of nearly 2500 species will be of the most interest. These directions are summarized in Chapter 20 and arranged in alphabetical order of the genera. A number of abbreviations are used in Chapter 20, and these are all explained at the beginning of that chapter.