27 



fully formed presents three well marked layers and is endowed with 

 a remarkable peculiarity of forming a kind of caryopsis with the wall 

 of the oogonium. 



Of the three layers formed in the wall of the oospore, the in- 

 nermost layer is of uniform thickness, while the other two layers are 

 irregular in outline and unequal in thickness ; and the outermost 

 layer which is the strongest of these three layers, usually remains 

 unthickened at the point just under the point of contact of the antheri- 

 dium to the oogonial wall (Fig. 11), and also at the point correspond- 

 ing to the point of attachment of the oogonium to the mycelial hypha 

 (Fig. 10). 



In the oospore we find a large central oil drop, a granular protoplasm 

 and an excentrically placed small refracting body of unknown nature 

 (Fig. 11). The oospore varies in size from 33.6 /i— 57.6 ft and are 

 produced in great number. 



Indeed the number of oospore found in a space of one square m.m. 

 of a diseased leaf roughly estimated by examining a series of micro- 

 scopical sections varies from 500-800, so that the number of oospores 

 in a leaf of median size amounts to an extraordinary number of no 

 less than 3500000. But this is the number of spores contained in a 

 single leaf, which are ready for germination for the future season. How 

 immense must be the number found in a single plant, a single raw of 

 the plants, or in a whole field of the plants! 



Most of the oospores consists of a single cell, but there are also 

 others which seem to be composed of two cells, and thus compound in 

 their nature (Fig. 11 b and f). However, if we study their develope- 

 ment, we soon see that the latter form of spores is nothing but two 

 distinct spores formed in a narrow intercellular space and adhering 

 together by mutual pressure so as to form a double cell much like the 

 winter-spore of some Puccinia. 



Besides, we sometimes find oospores or oogonia which contain two or 

 three small spore-like bodies of a globular shape which are also found 

 outside the spore (Fig. 11 g-f). What are these spore-like bodies? 



To answer this question, I put some quantities of these spores 

 in a Petri's disk, containning a nutrient solution and watched their 

 germinatian from time to time. To my astonishment, these bodies 

 proved themselves to be encysted infusoria which on hatching gave 

 rise to Paramaecium. 



