STRUCTURE OF A SPORE OF MILDEW. 77 



brane on the external surface becomes thickened, and the 

 whole increases in breadth. Within the sheath is found 

 transparent matter, from which a number of little spherical 

 bodies or very minute growing particles like those observed 

 within the spheri car spore may be obtained. It may be 

 that as this process grows at one or more points a thinning 

 occurs in its wall, and a portion of its contents coming into 

 more immediate contact with the pabulum increases in 

 amount, and thus gives rise to the production of another 

 branch or process which grows exactly like the first. 



Now, how does this simple organism nourish itself? 

 The materials for its growth and nourishment are certain 

 inanimate matters (solids and gases) existing dissolved in 

 fluid in which the organism floats. These materials must 

 pass into its structure and become part of it. That which 

 is inanimate must become incorporated with and assume 

 the properties of living matter. Now if such a living thing 

 be placed under certain unfavourable conditions its vital 

 properties will be destroyed. The transparent living matter 

 in its interior will shrivel up and die, but this will be 

 attended by no obvious alteration in the external mem- 

 brane. The part which exhibits form (formed matter) 

 remains; that which is without form (living matter) is 

 destroyed. 



In the growth of the structure, then, how is the new 

 matter produced ? Does it take place by deposition upon 

 the external surface of the investing membrane, or is the 

 new matter produced by the soft formless matter in the 

 interior? To put the question still more simply, Is the 

 capsule, the so-called cell wall, formed by deposition of 



