THE STRUCTURE OF THE SEED 35 



of potting and that rough measure of repair the seed had 

 improved upon by forming a fibroid layer to cover the hole, 

 rendering it continuous with the inner membrane. 

 In section it appeared thus : 



.-,J^tw^/ai/er 



That, to my mind, sufficiently proved the point. The 

 insulation of the seed must be intact if germination is to 

 take place and I imagine that the plug of clay filled the 

 temporary purpose of enabling metabolism to proceed. 



We have duly noted the fact that the seed requires warmth 

 as well as moisture and oxygen to enable it to germinate 

 and the degree of warmth is, I take it, in accordance with 

 the chemical secretion and physical structure of the seed. 

 In cold weather not only is the resistance of the electrolytes 

 in the soil increased so that less current is present in the 

 environment of the seed, but the resistance of the liquid 

 content of the seed substance is also enormously in- 

 creased ; two conditions which militate against that full 

 measure of electrification upon which germination is 

 dependent. Free oxygen has the same important part 

 to play in development — from the pollen to the mature 

 plant — as it has in the development of the animal cell into 

 the adult animal body. As the mother of the unborn child 

 could not sustain life in it or in herself without oxygen 

 for the generation of nerve force, so the mother plant needs 

 it to reinforce the supply to the ovules and to the seeds, 

 while the seeds themselves could not develop the plumule 

 and therefore become plants without it. 



So far I have only spoken of the seed coat as the outer 

 coating of tinfoil of the Leyden-jar, but it undoubtedly has 

 other uses and purposes, such, for instance, as affording 

 protection from enemies and from accident, and particularly 

 in preventing an excess of moisture from reaching the inner 

 membrane and so tending to break down its resistance, 

 although this danger is specially guarded against by its 

 composition. 



