934 



SCIENCE. 



[N. S. Vol. XVI. No. 415. 



long as that of a corresponding weight of 

 glucose; it can serve tmce as long for the 

 nutrition of the same weight of plant. 



These remarkable results lead us to the 

 consideration of the mode in which the 

 carbohydrates, and particularly the sugars, 

 are assimilated by the plant. We have held 

 the view that the sugar molecule is capable 

 of entering with little if any alteration 

 into that of protoplasm. We have found 

 no direct evidence bearing upon its fate. 

 It is possible to detect sugar in the axis of 

 a plant till quite near its growing point. 

 Then the reaction ceases to be obtainable, 

 and we know that assimilation is taking 

 place. But we have still to investigate 

 the steps, no very easy problem to under- 

 take. May it possibly be that it is the 

 alcohol moiety of the sugar which the pro- 

 toplasm takes up, part of the carbon dioxide 

 evolved by the growing organ being an ex- 

 pression, not of respiration, but of a fer- 

 mentation preliminary to assimilation? 



But I feel I have dealt at sufficient length 

 with this question. I pass, therefore to con- 

 sider briefly another nutrition problem of 

 a rather different kind. The germination 

 of seeds is a qiiestion that might be thought 

 to have been fairly settled by the investi- 

 gations of the latter half of the last cen- 

 tury. We have come to the conception of 

 the seed as fundamentally a young embryo 

 lying quiescent within its testa, and pro- 

 vided with a store of nourishment deposited 

 either within its own substance, or lying 

 round it in the tissues vaguely named en- 

 dosperm or perisperm. The nourishment 

 has been held to be practically ready for its 

 use, needing only a certain amount of 

 enzyme action to be applied to it to convert 

 the food store from the reserve to the nu- 

 tritive condition. We have recognized here 

 starch, proteids and giucosides, and have 

 ascertained that the embryo can furnish the 

 .appropriate enzymes for their digestion. 

 Each reserve store has apparently been 



quite independent of the rest, and the em- 

 bryo has had control of the whole. 



Certain considerations, however, lead us 

 to the view that for albuminous seeds at 

 any rate this mode of looking at the matter 

 is no longer satisfactory. We may first 

 ask how far the embryo is the controlling 

 factor in the digestion. Putting the matter 

 in another form, is the influence of the 

 parent plant lost when a stable store of food 

 has been provided for the offspring, and 

 does it leave its utilization entirely to the 

 latter? Is the gametophyte prothallus 

 merely to become a dead or inactive struc- 

 ture as soon as it has developed its young 

 sporophyte, or may its influence extend for 

 the longer period of germination? There 

 are many reasons for thinking this is the 

 case. Indeed the view has been put for- 

 ward by some observers at intervals for 

 some years. Gris claimed to have shown it 

 in 1864 ; but it was opposed by Sachs, who 

 said that the enzymes which cause decom- 

 positions in the reserve materials are always 

 formed in the young plant or embryo and 

 are excreted by the latter into the endo- 

 sperm. Some careful experiments on the 

 point were conducted by Van Tieghem and 

 were published by him in 1877. His work 

 was carried out on the seeds of the castor- 

 oil plant. He deprived the seeds of their, 

 embryos and exposed them for some weeks 

 on damp moss to a temperature of 25-30° 

 C. After several days of this exposure 

 he found the isolated endosperms were 

 growing considerably, and at the end of a 

 month they had doubled their dimensions. 

 In the interior of the cells he found the 

 aleurone grains to be gradually dissolv- 

 ing, and the oily matter to be diminishing, 

 though slowly. The dissolution extended 

 throughout the mass of the endosperm, 

 and was not especially prominent in the 

 side that had been nearest to the cotyledons. 

 He noted, too, that though starch did not 

 normally appear in the germinating endo- 



