22 Messrs. Brown and Escombe. On the Depletion of the 



We can in this case only detect a small amount of disintegration 

 immediately under the " grafted " embryo, and even after eight or 

 ten days this is not found to proceed for more than 0'5 to 1 mm. from 

 the " depleted layer." There is a partial but very incomplete cyto- 

 hydrolysis of the cell-membranes constituting the " depleted layer," 

 and a similar imperfect action can be traced microscopically in the 

 amyliferous cells as far as the disintegration has proceeded. The 

 starch-grains of the amyliferous cells immediately underlying the 

 " depleted layer " show unmistakable signs of attack by normal sub- 

 scutellar u pitting " without any admixture of that particular form of 

 erosion which is characteristic of the action of the " aleurone-layer." 



There can be no doubt that we here have further proof that the 

 embryo, by means of the secretion of enzymes from its scutellar 

 epithelium, is able to attack starch, and to assimilate the products of 

 its hydrolysis. Abundant proof of this fact was brought forward in 

 the 1890 paper, in which were described many experiments on the 

 artificial nutrition of excised embryos, and this fact has been amply 

 confirmed by Griiss in a series of very careful experiments he has 

 recently described.* 



It will be remembered that when embryos were cultivated on 

 gelatine in which starch-granules had been suspended, it was found 

 that a secretion of diastatic enzyme took place from the epithelial 

 cells of the scutellum, which manifested itself by erosion of the 

 starch, and that this erosion gradually extended to a relatively con- 

 siderable depth in the gelatine medium. That this action does not 

 proceed with the same rapidity in " dead " endosperms, on which 

 embryos have been grafted, is due to a great extent to the fact that 

 in this latter case the starch-grains are locked up in cell-membranes 

 which retard the diffusion of the highly colloidal diastase. Until 

 these cell-membranes are broken down we have not the most favour- 

 able conditions for a rapid formation of soluble nutriment from the 

 reserve materials, especially as the amyliferous cells appear to be 

 devoid of any power of initiating such changes autonomously. One 

 of us was originally of the opiuionf that the necessary cytohydrolytic 

 function resided in the embryo itself, and that it was manifested by 

 the same epithelial cells as those which produce a very active form 

 of diastase, but our more recent experiments have clearly shown that 

 this power of the embryo was much overrated, and that the greater 

 part of the cytohydrolytic process preliminary to the amylohydro- 

 lytic is due to the cells of the " aleurone-layer," the treatment to 

 which the grain was subjected in 1890 not having been sufficient to 

 completely destroy the vitality of these cells. 



This layer is the only part of the endosperm which can be recog- 



* ' Pring8heim's Jahrb.,' vol. 30, 1897, p. 645. 

 f Loc. cit., 1890. 



