76 COMPARATIVE MORPHOLOGY OF FUNGI 



In P. proliferum the sporangia are, as in many Saprolegniaceae, renewed 

 by proliferation, which may be repeated until almost all the protoplasm 

 has been used up in the formation of zoospores (Fig. 45, 7). In the 

 conidia formation of P. intermedium, the sporiferous hypha continues in 

 its growth under the terminal conidium, pushes it aside and terminally 

 cuts off a new conidium : this process may be repeated, resulting in race- 

 mose groups of conidia (Fig. 45, 13). Also the conidia may be cut off 

 successively in moniliform chains (Fig. 45, 14). 



In Phytophthora, only conidial forms are known. These conidia 

 are renewed like those of Pyihium. There is cut off terminally on each 

 of the extramatrical hyphae, a conidium which is pushed aside by the 

 developing hyphae, and falls off, as described for Pyihium intermedium 

 (Fig. 45, 13). 



In the higher Peronosporaceae, differentiation has extended to the 

 sporiferous hyphae. Just as the sporangia, which are firmly attached to 

 the mycelia and hardly to be distinguished from them, result in morpho- 

 logically and biologically differentiated conidia which break loose from 

 the mother plant and fulfil a new function — that of dissemination — their 

 sporiferous hyphae develop to differentiated conidiophores. The 

 extramatrical hyphae no longer cut off conidia and when brought to any 

 nutritive substrate, themselves develop to mycelia, but they represent 

 characteristically formed sporophores which perform this function 

 exclusively. They no longer develop indefinitely as typical hyphae, 

 but limit their growth and only when the conidiophore is mature, does 

 the terminal abstriction of conidia occur. Because this limited growth 

 permits only one conidium to be cut off from a hypha, only those forms 

 have been retained in which this loss is compensated by other adapta- 

 tions. In this respect, two types are known, that of the Albugineae 

 and that of the Peronosporeae. 



Albugineae. — The sporiferous hyphae of Albugo, as those of the 

 Pythieae, are simple. They differ from them in the limitation of growth, 

 in their thicker membrane at the base (Fig. 46, 5) and in the peculiarity 

 that several conidia are cut off at a hyphal tip in basipetal sequence, as in 

 Pyihium intermedium. From the hyphae which grow luxuriantly through 

 a substrate, a few nuclei enter the young sporiferous hypha and, sur- 

 rounded by thick protoplasm, migrate to the tip. When five to seven 

 nuclei have collected, the tip is abjointed and rounds off as a conidium. 

 The septum is laid down as a ring from the hyphal wall to the middle (Fig. 

 46, 1 and 2) ; it is differentiated subsequently into three layers, two outer, 

 deeply staining with haematoxylin, and a central one which takes 

 up a small amount of dye (Fig. 46, 3 and 4). After the conidium has 

 rounded off, the original hyphal wall dissolves at the constriction; a 

 conidium and hypha are only connected by the plate. The distal outer 

 layer of the plate is let into the conidial wall, the proximal outer layer 



