110 



PHYCOMYCETES. 



and the formation of zoosporangia take place in the cells of the 

 living host-plant. In addition, spores are formed which have 

 a resting period. 



{B) Only one kind of spore is formed ; it has a resting period, 

 and only proceeds to produce sori of zoosporangia after decay 

 of the host-plant. 



(a) Ghrysochytrmm : protoplasm contains a yellow oil. 



(b) Leucochytrium : protoplasm colourless. 



Each of these divisions is sub-divided into forms with simple 

 vesicles, and those with compound. 



Mesochytrium. 



Synchytrium (Pycnochytrium) succisae, De Bary and Wor.^ 

 This parasite forms warty swellings and yellow spots, generally 



% 



-ft 



-■^R'^r 



Fig. 2G. — Synchyti-ium succUae. A, A mature sporocarp inside its host-cell. 

 £, In the upper part of the cell a sorus of swarm-sporangia after escaping frooa 

 its covering, which lies below it. C, Isolated swarm-sporangium. D, Swarm- 

 spores. (After Schroeter.) 



on the radical leaves and base of stem of Scahiosa succisa. 

 Infection is brought about in damp situations by means of 

 swarm-spores. These have a single cilium, and bore their way 

 into the host-cell. ASter entrance, they produce a plasma-mass, 

 which becomes enclosed in a delicate membrane. The cell so 

 formed sprouts at its uppermost pole, and gives rise to a new 

 spherical ceU, into which the older discharges itself. In the 

 second cell numerous small sporangia are formed, so that it 

 represents a sporangial sorus ; beside it is always found the 

 empty membrane of the first cell. The sorus breaks up later 

 into single sporangia, which on opening, set free their contents 



^ Schroeter, " Pflanzenparasiten aus d. Gattung Synchytrium.'' Cohn's Beitr, ;. 

 Biolog. d. Pflanzen, 1875. 



