OOMYCETES 



333 



emerge again outside the oogonial wall, but they remain closed at all 

 points, and after a day or two perish. In the case of certain species, the 

 antherids never produce these pro- 

 cesses, or the oogones may be 

 without antherids. In other cases 

 antherids are never produced at all, 

 or only by way of rare exception. 

 In the meantime the oospheres ripen 

 into oosperms, while the antherids, 

 if present, perish. Pringsheim has 

 recently endeavoured to show that 

 impregnation takes place in certain 

 species by the transference into the 

 oospheres of minute portions of 

 antheridial protoplasm moving in 

 amoeboid fashion. De Bary points 

 out that, while Pringsheim has not 

 actually seen this, the sole evidence 

 trusted to is that of stained prepa- 

 rations, which appear to exhibit open 

 communication between antherid 

 and oosphere, &c. In any case the 

 observation does not affect those 

 cases where antherids are either want- 

 ing, or do not produce the penetrating 

 tubular processes. 



The ripe oosperms thus parthe- 

 nogenetically produced germinate 

 after a period of rest varying from 

 a few days to several months. Ger- 

 mination takes place, as in the 

 Peronosporese, either by means of 

 a germ-tube, or zoospores are pro- 

 duced. 



Propagation is effected by the 

 agency of zoospores produced in 

 special zoosporanges, and also excep- 

 tionally by means of certain resting- 

 cells formed by the- mycele after 

 transverse division of the hyphas 

 (Saprolegnia). These swell out into globular form, with thick mem- 

 branes and plentiful protoplasm, and germinate by the emission of a 

 germ-tube, or zoospores are formed in them ('resting sporanges' of 



FIG. 5291. A to C, Achlya racemosa Hildebr. 

 At the end of A is an empty zoosporange, j. 

 with empty zoospore membranes ; at a. b, and 

 c, are ocgones with antherids, a, in an early 

 stage, b and c as in , oogone with two 

 oospheres and an antheridial tube applied 

 to one. C, ripe oosperm. Z>, , Achlya. 

 polyandra Hildebr. D, oosperms germinat- 



ing. E, germinating oosperm which has formed 

 a sporange with a head of spores. {A x 145. 

 B and C x 375, D and E x 225.) (After 



