76 SCIENCE PROGRESS. 



the experiments on the artificial nutrition of leaves by- 

 solutions of carbohydrates, published by A. Meyer in 1886 

 (24), and by Laurent in the same year (25), and by those 

 of Acton (26) on the absorption under abnormal conditions 

 of organic compounds by the roots of various culture plants. 

 All these observers have shown that when the only source 

 of carbon that was afforded to the plants with which they 

 experimented was a weak solution of cane-sugar, the latter 

 was gradually absorbed, and in due course starch made its 

 appearance in the cells of the parenchyma of the leaves. 

 The experiments of Brown and Morris on the artificial 

 feeding of isolated barley embryos (29) with solutions of 

 cane-sugar also support the view that the latter may readily 

 give rise to starch. In these experiments excised em- 

 bryos were deprived of starch by an exhaustive water 

 culture of five or six days, and then placed upon dilute 

 solutions of cane-sugar, and starch was speedily formed in 

 the cells of the scutellum. 



Since Schimper's classical researches upon the mode of 

 formation of starch grains, their appearance has been attri- 

 buted uniformly to the action of plastids, either leucoplasts, 

 as in parts not exposed to light, or chloroplasts, in the 

 illuminated regions. The striation of the larger grains has 

 consequently been held to be due to apposition of succes- 

 sive layers upon the surface of the grains. Recent writers 

 claim, however, that this view is insufficient, and that 

 probably in many cases the deposition is effected by the 

 immediate action of the protoplasm of the cell. 



The leucoplast theory is undoubtedly a good deal 

 strained by the cases where immense numbers of very 

 small grains, hardly larger than mere specks, make their 

 appearance in rapidly growing structures, particularly as 

 even high powers of the microscope fail to show the 

 presence of any plastid before or during the deposition. 

 In the pollen grains of many plants before their germina- 

 tion, and in the pollen tube as it develops, small specks of 

 starch make their appearance. In the pollen of Zamia 

 skinncri the ungerminated grain shows a fairly homo- 

 geneous protoplasm, scarcely even granular. When this 



