138 DIVISION II.—COURSE OF DEVELOPMENT OF FUNGI. 
intervals; accidental and unimpertant. 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. 
(4) In the majority of species they send out a germ-tube directly either from their 
extremity or laterally, and never form swarm-spores. 
(c) In the plasmatoparous species mentioned on page 112 there is an intermediate 
form between (a) and (4) which is especially allied to the variety of (4) in which there 
is an apical germ-tube. ‘ 
Cystopus. Gonidia are abjointed in along 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! 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 
nating, i. e. forming swarm-spores ; the protoplasm is already divided. D escape of Peronosporeae as at present 
ecm A an re te nae cman Fine ne im determined. entirely agree 
trated into a stoma of Lepidium sativum ; it is the inner surface of the stoma or with those described above 
epidermis which is seen, and the spores from which the germ-tubes come are on the E a 5 . 
outer surface at the stoma. Magn. 400 times. in the points with which we 
are here concerned. 

FIG. 66. Cystopus didus, Lév. B idioph C gonidia in the act of germi- 


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 

1 Second Mémoire sur les Uredinées in Ann. d. sc. nat. ser. 4, IJ, p. r10. 
