INTRODUCTIONElectron micrographs of the primary cell wall in the growth-zone of Phycomyces sporangiophores show an isotropic network of chitin fibrils on the outside and an almost transverse structure on the inside (3,8). The same applies to the cellulose fibrils in the cell wall of staminal hairs of Tradescantia (10). Axial orientation of the outer fibrils is apparent in the primary cell wall of growing cotton hairs, which on the inside again show a more or less transverse structure (5,9).The present paper reports the finding of a similar architecture in the growing hairs of two more plant species, viz. Ceiba pentandra var. caribaea and Asclepias cornuti. Furthermore some new E.M.-graphs of cotton hairs are presented, since those published earlier were of a low standard. Obviously because the present E.M.-graphs revealed more details, we were struck by a particular common feature in the fibrillar structure which led to some deductions regarding the process of cell wall extension in plant hairs and in the Phycomyces sporangiophore. These will be discussed in the last section.
METHODSFruits, gathered at definite intervals after flowering, were preserved in alcohol *.If the hairs of young fruits were viewed in radial direction between crossed nicols, a negative double refraction with reference to the cell axis was found. This always occurs in growing tubular cells, at least in growing regions of such cells. Of course, hairs of nearly full-grown fruits were always entirely positive.With Ceiba, negative double refraction was found in the sample of 25 days and in all younger ones, the next sample being 35 days old. * We are greatly indebted -to the manager of Siloewok Sawangari estate, Java, who furnished the Ceiba material. Asclepias and cotton were grown in our botanical garden.
PRIMARY CELL WALL IN PLANT HAIRS AND PHYCOMYCES SPORANGIOPHORE 219In order to be sure that the sample to be used for the electronmicroscopy would contain primary cell walls only, fruits gathered ca 20 days after flowering were taken. The mean hair length was roughly 12 mm as against 25 mm in the 35 days sample.The Asclepias hairs were negatively birefringent up to 35 days, though less distinctly than after 28 days. Hairs of 21 days old were used for the E.M.-work. Like those of Ceiba they were negative from the extreme tip down to base. Their length was 8 mm as against 30 mm in the 35 days sample.The cotton hairs used, were 15 days old and were from the same fruits as used in earlier work (9). Of these hairs too, the extreme tips were negatively birefringent.The hairs were cut off, suspended in 70 % ethanol and cut into pieces of 30-60 μ length by means of a small electric blendor. The ethanol and all other liquids used, had previously been freed from dust, etc. by centrifuging.The fragmented hairs were centrifuged and then cleaned by the following successive treatments, alternated with centrifuging in water:a. 30 min. in perhydrol-glacial acetic acid 1 :1 at 100° C, b. 20 min. in 2 % sulfuric acid at 100° C, c. 20 min, in 2 % NaOH at 100° C...