OOSPORES. 135 



ferce, as white, blister-like patches, the conldia are produced 

 just beneath the epidermis, which becomes ruptured, and 

 allows their escape. In Peronospora, as the Grape-Mildew 

 (P. vHicola), the Potato Fungus (P. infestans), the white, 

 frost-like down on Peppergrass (P. paradtioa), etc., the 

 conidia are produced on aerial branches of the hyphse 

 growing from the stomates (Fig. 250). The conidia 

 quickly germinate, and in some species give rise directly 

 to a filament ; in other species, swarm-spores, each with 

 two cilia, are formed, which, after coming to rest, send out 

 germinating filaments ; these pass into the host-plant, 

 either growing through the stomates, or boring directly 

 through the epidermis, where 

 numerous hyphse are again pro- 

 duced. The sexual reproduction 

 takes place by means of oogonia 

 and antheridia (Fig. 247). 



169. The Fucoidese are also 

 representatives of the Oosporese. 

 They are marine Algse, whose 

 green, or chlorophyll, is con- 

 cealed by a reddish-brown color- 

 ing matter. They are often of ^^ 

 great size and present considerable differentiation of tissue, 

 not found in the Thallophytes previously mentioned. They 

 may be flat, or strap-shaped, and several yards in length, 

 as in Laminaria ; they may be tree-like iu form and size, 

 twenty to thirty feet in height, as in Lessonia ; or, like a 

 gigantic pinnate leaf, sometimes more than three hundred 

 feet long, as Macrocystis. The outer tissues are generally 

 dense, and formed of small and crowded cells ; the inner 

 cells are mostly elongated and loosely joined, so as to 



Fig. 250. Conidia of Peronospora ; /i, hyphie ; s/^ conidia ; j/, stomates ; ^df 

 guard-cells. 



