106 Mary Gordon: 



outer layer ceases to divide, but it persists in the seed as the 

 aleurone layer. Even when the cells of this layer are resting, 

 and have become filled with reserve food, their nuclei remain 

 large and intact. At this stage the walls of the aleurone cells 

 become considerably thickened, and this supports the cambium 

 theory, since cambial cells entering on a period of rest show 

 thickenings on their walls which are either partly or wholly 

 removed when such a layer recommences its activities. 



I have attempted here to trace the development of the 

 aleurone layer and the starchy endosperm in the more common 

 cereals, and to show whether the starchy endosperm is 

 developed from the aleurone layer or not; that is, to prove 

 whether the aleurone layer is really an endospermic cambium 

 or not. 



The ovules of barley, wheat and oats were taken at various 

 stages of development, and fixed in either Carnoy's or Bouin's 

 fixing solutions. Considerable difficulty was experienced in 

 fixing the oat grains, owing to the hairy nature of the pericarp, 

 which prevented the fixing solution from penetrating the seed. 

 An attempt to fix some seeds under reduced atmospheric 

 pressure was not any more successful, since the more volatile 

 •constituents of the fixing solutions tended to vaporise under 

 the reduced pressure, and so pass out of the solution. The 

 •only way to ensure rapid and complete penetration of the fixing 

 solution is to pierce the seed-coat, and even then the inner 

 endosperm of ripe grains generally breaks in cutting. Micro- 

 tome sections were cut of the grains embedded in parafifin, and 

 the sections were stained with Haidenhain's Iron Haematoxylin 

 as it rendered the nuclei in mitosis very distinct. In all three 

 •cases the development was found to be practically identical, 

 except that the ripe barley grain has — as is well-known — an 

 aleurone layer several cells deep, whereas w^heat and oats have 

 a single layer only. In the "Annals of Botany," Miss Brenchley 

 has published two papers describing the earlier stages in the 

 development of the grains of wheat and barley (3) and (4). They 

 show how the first endospermic nuclei are formed by the 

 division of the secondary nucleus of the embryo-sac, but the 

 later stages in the endosperm development are not described. 



A longitudinal section of a young ovary is shown in Text 

 Fig. I. ; it is not cut directly through the centre of the seed so 

 that the embryo does not appear in the section. In the centre 



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