14 WHAT THE PLANT IS MADE OF [chap. 



all the resources of wheat and barley. A few simple 

 experiments with seeds of various sizes, sown at different 

 depths in pots, will show how the proper depth for each 

 seed is conditioned by its weight, i.e. by the amount of 

 material it has available to lift a leaf up into the light. 

 Some covering of soil is desirable in order to keep the 

 seed from drying out ; as far as the light goes it does 

 not much matter, for all our common seeds germinate 

 equally well in light or darkness. 



One other point in the germination of seeds requires 

 consideration : the materials in the food store of the 

 endosperm or cotyledons are mostly insoluble, as we 

 can convince ourselves by a little experiment ; they 

 consist as a rule of starch and proteins, with sometimes 

 fat and oil. Yet when the embryo begins to grow these 

 materials have to be conveyed to the end of the shoot 

 where leaves are unfolding, and to the growing tip of 

 the root ; that they do get transferred is proved by the 

 eventual emptying of the endosperm or cotyledon. 

 The transference is only possible if the food store is 

 first of all rendered soluble in water, for liquids alone 

 can traverse the cells of the plant. The mechanism of 

 the process can only be rendered intelligible by another 

 experiment or two. Soak a handful of barley in water 

 as before, and put it aside in a warm place to germinate 

 until the rootlets are an inch or so long ; now smash the 

 grains up in a mortar, add enough warm water 

 (at 40° to 50° C.) to make up a sort of thin porridge, and 

 let the whole stand for an hour or two, then filter. 

 Meantime make some starch paste by rubbing up a 

 few grammes of starch with cold water, and pouring 

 on 300 to 500 c.c. of boiling water; then bring the 

 whole up to a boil, and put it aside to cool. The starch 

 paste will form a thick, troubled-looking liquid, and if 

 to a little of it in a test-tube a drop of a solution of 



