OBSERVATIONS ON THE GENUS PYTHIUM. 507 



At 8 a.m. next day (g) no signs of germination were apparent.; 

 the very large granules were now dull, and their protoplasmic 

 matrix evidently becoming pale and disorganised. Fig. 27 (h) 

 however, shows the normal course of events in another speci- 

 men: the zoospore, after about five-and-twenty minutes of 

 active life, had come to rest (as in fig. 27, d), and at once pro- 

 truded a short process. Within an hour after this, the stages 

 i and k were passed through ; the granules becoming used up 

 in the elongating germinal tube, and a vacuole forming in the 

 spore, which became larger and larger as its contents were 

 drawn upon. Soon after the stage k — the tube having reached 

 its highest state of development at the expense of the proto- 

 plasmic and granular contents, and having met with no suitable 

 matrix to enter — the whole perished. Such zoospores, 

 attached to the cuticle of a cress-seedling killed in hot water, 

 germinated in the same manner, the germinal tube, however, 

 entering the cell wall (fig. 28), and extending as a mycelium in 

 the way described previously. 



On cress-seedlings which had been killed by hot water, and 

 which had been brought into contact with some debris contain- 

 ing Py t hi um given to me by Prof. De Bary, I observed the 

 development of numerous zoosporangia of the typical P. 

 gracile already described, together with a much smaller 

 ->jiumber of a second, hitherto undescribed form of zoosporan- 

 gium. Attempts were at once made to separate the two forms 

 in the following manner, by a method often successfully em- 

 ployed in similar cases, and which may be described in detail, 

 because it is instructive in many ways. 



A small portion of the semi-rotten cress-seedling was selected, 

 on which a young zoosporangium of the required Pythium 

 was observed to be preparing to emit its zoospores. This 

 was teased Avith needles in the hope of removing all the zoo- 

 sporangia of P. gracile. This done, the cleaned specimen 

 was placed in contact with a freshly killed cress-seedling in a 

 drop of pure water on a perfectly clean glass slip. As in all 

 these experiments, every precaution was taken to avoid acci- 

 dental infection, by heating the needles, forceps, &c., and of 



