MAY 21, 1927] NATURE 745

Occurrence of Branched Hairs in Cotton and upon a longer base than the former. Hairs with shorter side branches can be seen in several places. The aossypium Stocksii. hairs on the seed coat of Gossypium Stocksii are IN the columns of NATURE of Mar. 12, p. 392, usually regarded as of the nature of ' fuzz.' In our Mr. N. W. Barritt describes branched hairs in a material they are some 8 mm. to 10 mm. long. specimen of Egyptian cotton. Such branched hairs It seems probable that in the modern forms of of Gossypium have been known to us for sorp.e time Gossypium the branched hair has become suppressed, and have been the subject of an investigation by us and usually develops only tardily and to a limited which we hope shortly to publish. extent in the form of ' fuzz.' We have growing here each year in our experimental We have Gossypium Stocksii from the Sind Desert area what is probably the most representative growing and flowering here now. There are several characters in it that have never been correctly described. In our material there are no signs of any stipular glands at the base of the clawed bracteoles as figmed in Watt's "Wild and Cultivated Cotton• Plants of the World." The flowers of om material, too, could not be describedas ' large ' ; in comparison with most other Asiatic cottons, they are small. In colour the flowers are pale sulphur yellow and of a totally different shade from that of Asiatic cottons generally. The pollen grains, in the character of their spines, differ from those of any other Asiatic Gossypium seen by us. An investigation has been made into the cytology of Gossypium Stocksii, and thirteen chromosome bodies have been found in the FIG. I.-Branched hair of Thespesia popttlnea, 0·9 mm. long. developing pollen grain. W. YouNGMAN. S. S. PANDE. Agricultural Research Institute, collection of Asiatic types of cotton to be found N agpur, India. anywhere in the world. Amongst several of these types, by the exercise of patience, we have found these branched hairs, as also in Upland American Intensities of Molecular Beams. and Sea Island types. The branched hair represents KNAUER and Stern (Zs. f. Phys., 39, 775) have a form of hair that occurred in the phylogeny of the recently investigated the relation between the Hibiscere. It is very well seen in Thespesia populnea, intensity of a beam of mercury molecules and the upon the seed coat of which there are hairs of at least pressure in the oven or source chamber. They have found that the intensity of the beam increased uniformly with the oven pressure, until the mean free path in the oven was about equal to the width of the oven slit. At this pressure the beam had a maximum intensity, becoming less intense as the oven pressure was increased above this optimum value. As an explanation of this maximum, they have suggested that the molecules emerging from the slit, at pressures greater than the optimum pressure, collide with one another, giving rise to the formation of a cloud in front of the slit. Instead of originating in the slit itself, the beam then has its source in this diffuse surface of low intensity. This explanation does not seem correct, when a consideration is made of the frequency of the collisions taking place between the molecules which have passed through the oven slit. An indication of the prob• ability of such collisions may be gained from a calculation of the free path in an ideal gas the mole• cules of which are moving in a single direction with a Maxwellian velocity distribution. The result of such a calculation shows that the mutual collisions between the molecules within the beam are so infrequent as to FIG. 2.-Branched hairs of Gossypium Stocksii. produce no appreciable effect on the intensity of the beam, except at oven pressures far greater than the two types, one of which is branched and another optimum pressure observed by Knauer and Stern. unbranched. The branched type is shown in the The diminishing intensity of their beam, as the pressure photomicrograph (Fig. 1). The length of this hair was raised above the optimum pressure, was more is 0·9 mm. probably due to scattering by molecules which had In Gossypium Stocksii, a type of cotton in some been reflected from the uncooled walls of the chamber respects primitive, hairs occur within the capsule between the slits. The reason for this statement will not only upon the seed coat but also upon the capsule appear from the following experiments. wall. Many of these hairs, both upon the seed coat A beam of mercury molecules was formed in a and the capsule wall, show branching. These are manner similar to that of Knauer and Stern, with the shown in Fig. 2. Coming off from the mass of important difference that the region between the two capsule wall shown in this photograph is a bifurcate slits was entirely surrounded by a liquid air cooled hair with a very short basal part embedded in the surface. In this way all molecules were removed from wall. To the left of this is another similar one with this space at their first impact with the walls, with the No. 3003, VoL. 119] x2

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