ZOOSPORES IN THE SAPROLEGNIEJI. 437 



3. The homogeueous stage is accompanied by a loss of 

 turgescence, and in many cases by a marked contraction of the 

 sporange. 



4. The clear spaces seen in the final separation are merely 

 the watery liquid of the sporange between the contracting zoo- 

 spores, and do not represent expulsive matter. No such expul- 

 •sive matter exists. 



5. The sporangial zoospores of Achlya possess at their 

 exit the two tractella described by Cornu, just like those of 

 Saprolegnia and Leptomitus. Achlya is therefore dipla- 

 netic. 



6. The escape of the zoospores is not due to any such expul- 

 sive matter as has been assumed^ but to the chemical stimulus 

 of the oxygen in the medium acting on the auto-motile zoo- 

 spores. 



It would seem probable that the escape of the protoplasm 

 from gonidia of so many Peronosporese (Phytophthora and the 

 plasraatoparous Peronosporae, for instance) is due to the same 

 chemical stimulus of well-aerated water. There is no evidence 

 for the existence of an expulsive matter in the sporange or spore 

 of any aquatic fungus. Sporangial walls being diffusible to 

 water and gases it is obvious that the conditions of the constantly 

 immersed sporange are totally different from those of the aerial 

 ascus of the higher fungi, where such a material does certainly 

 exist. 



The above observations were chiefly made on plants grown on 

 mealworms in tumblers, and floated out on large glass slides for 

 observation, seldom covered, and replaced in the tumblers after- 

 wards. In some cases I have used small cultures in the hanging 

 drop with the cardboard or blotting-paper moist chamber. 



P.S. — A suggestion as to the physiological value aud 

 the filiation of diplanetism, &c., may not be out of place. The 

 zoospore on leaving the sporange has enough reserve material 

 to carry it a certain distance, and to enable it to germinate. 

 In the first swarming the zoospores get scattered ; and then 

 during the long stage of encystment the further work of dis- 



VOL. XXVII, PART 3. NEW SER. H H 



