Oct. is, 1920 Mustard Seeds and Substitutes: I. Chinese Colza 123 



The surface usually appears smooth (PI. 10, A, B) but under a hand 

 lens shows very weak reticulations on the yellow seed and more distinct, 

 but by no means prominent, reticulations on the brown seed (PI. 10, C, D). 



In cross section under the microscope the epidermis of the seed coat 

 (PI. 10, E, F, a) is striated tangentially, does not show any cell structure 

 as in the mustard seed, and is about 5 microns thick. It does not swell 

 appreciably when moistened and does not show crosses with polarized 

 light. The sclerenchymatic palisade cells (PI. 10, E, F, c) vary more in 

 height in the brown seed than in the yellow. This explains the 

 presence of the more pronounced reticulations in the brown seeds. 

 For the yellow seed the height is almost uniformly 20 microns, while 

 the average for the brown seed is about 25 microns, with a maximum 

 height of 31 microns. The limits found for all the seeds were 15 to 31 

 microns high by 8 to 15 microns wide. The cell walls are strongly 

 thickened at the base and sides, and the inner walls are smooth. The 

 lumen contains no color substance. The parenchyma, always developed 

 to one or more rows in the Brassicas (40, p. 615), is compressed to such an 

 extent that it appears to be almost entirely lacking (PI. 10, E, F, b). 

 In Brassica nigra one row and in Sinapis alba two rows of parenchymal 

 cells are clearly visible, even in the mature seeds. 



The parenchyma (PI. 10, E, F, d), located below the palisade cells, 

 consists mainly of one row of cells which in the yellow seeds contain 

 no color substance but in the brown seeds are filled with pigment. The 

 endosperm (e) is characterized by the protein layer, a row of cells usually 

 one cell wide, but occasionally two cells wide, the cells varying in height 

 from 15 to 21 microns and in width from 15 to 42 microns and contain- 

 ing protein masses. The tissue (/) located below this layer is composed 

 of several layers of parenchyma cells which, especially in the mature 

 seeds, are strongly compressed. The embryo consists of two cotyledons 

 folded in a characteristic way around the radical. The tissue is paren- 

 chymatic or meristematic. The cells which form the cotyledon tissues 

 are not characteristic except that they contain globules of fatty oil, 

 protein masses, and, especially in the immature state, a limited number 

 of small starch grains which range in size up to about 6 microns in 

 diameter. Experiments to locate the glucoside as a crystalline body 

 have been unsuccessful. Studies to locate the enzym and glucoside 

 microchemically in the cells are being undertaken. 



DESCRIPTION OF THE PLANT 



Experiments in the growth of selected yellow and brown seeds were 

 made under greenhouse and field conditions. The field experiments 

 were made at Arlington, Va., during the summer of 191 6, and at Yarrow, 

 Md., during the summer of 191 7. The laboratory records, so far as 

 differences in stages of growth are concerned, are more complete for the 

 plants grown in the greenhouse. 



