i 3 8 



DIVISION II. COURSE OF DEVELOPMENT OF FUNGI. 



intervals; accidental and unimportant deviations from this plan are sometimes but 

 rarely observed. The gonidia are usually abjointed as spores, and in germination* 

 which takes place under water, become swarming sporangia. The swarm-cells are not 

 formed in the same way as in Pythium but inside the original membrane of the 

 sporangium, from which they issue through an aperture at the apex. As a frequent 

 exception the germination of the spores abjointed from the gonidiophores is direct by 

 the growth of a germ-tube. 



Peronospora. Gonidiophores, disposed as in Phytophthora and regularly and usually 

 copiously branched, give off by abscision a single spore at the extremity of every branch 

 and then die away. The gonidia germinate in water and the process varies in different 

 species. 



(a) In a number of species they behave as in Phytophthora. 



(b) In the majority of species they send out a germ-tube directly either from their 

 extremity or laterally, and never form swarm- spores. 



(*:) In the plasmatoparous species mentioned on page 112 there is an intermediate 

 form between (a) and (b) which is especially allied to the variety of (b) in which there 

 is an apical germ-tube. 



Cystopus. Gonidia are abjointed in a long simple chain from the apex of club-shaped 

 branches arranged in tufts (Figs. 66 and 33). The branches are set close together and 

 parallel to one another and form broad hymenia (see section XII). The gonidia in 

 germination form swarm-spores only ; the terminal member alone of each chain, except 

 perhaps in C. candidus, may behave otherwise ; it has a thicker wall than its younger 



sisters and is poor in proto- 

 plasm and incapable of ger- 

 mination. Tulasne's state- 

 ment 1 regarding the peculiar 

 form of the terminal members 

 in C. Portulacae and its send- 

 ing out a germ-tube has not 

 been confirmed. As the goni- 

 dial chains of Cystopus begin 

 to develope beneath the 

 epidermis of phanerogamous 

 plants and afterwards force 

 their way through it, the 

 thick-walled terminal mem- 

 bers evidently serve to protect 

 their younger sisters behind 

 them. 



The other genera of the 

 Peronosporeae as at present 

 determined entirely agree 

 with those described above 

 in the points with which we 

 are here concerned. 



In all the above cases each germ-tube proceeding from a gonidium either 

 directly or through the intervention of swarm-cells developes on a suitable substratum 

 into a thallus, which first forms gonidia and ends with the production of oospores. 

 If the conditions are less favourable the plant forms often a luxuriant thallus, and 

 abundance of gonidia through an unlimited number of generations proceeding from 



FIG. 66. Cystopus Candidus, Lev. B gonidiophores. C gonidia in the act of germi- 

 nating, i. e. forming swarm-spores ; the protoplasm is already divided. D escape of 

 the swarm-spores. E swarm-spores in the motile condition. F swarm-spores come 

 to rest on a microscopic slide and germinating. G two germ-tubes which have pene- 

 trated into a stoma of Lepidium sativum ; it is the inner surface of the stoma or 

 epidermis which is seen, and the spores from which the germ-tubes come are on the 

 outer surface at the stoma. Magn. 400 times. 



1 Second Memoire sur les Uredinees in Ann. d. sc. nat. ser. 4, II, p. no. 



