144 DIVISION II. COURSE OF DEVELOPMENT OF FUNGI. 



of species which agree with Achlya in other respects have the last named peculiarity 

 alone, and their spores do not collect into heads ; these are included under the generic 

 name of Dictyuchus. Some histological details will be found in section XVIII. 

 The formation of swarm-spores in the germination of the oospores agrees in every 

 known instance with the character assigned to the genera, but has not yet been observed 

 in Dictyuchus. 



Aplanes, a new genus, identical probably with Reinsch's Achlya Braunii, very 

 rarely forms gonidia on the developed thallus, but more often in the germination of 

 the oospores. The gonidia are formed as in other genera ; in the germination of the 

 oospores either directly in the cavity of the oospores, or in a single row in sporangia 

 on short-lived dwarf plants. They put out short germ-tubes at once in the place 

 where they are formed, nor have I ever been able to perceive any appearance of 

 swarming. 



Resting gonidia. In old tufts, those of Saprolegnia especially, it not unfrequently 

 happens that the thick thallus-tubes become broken up by transverse walls into cylin- 

 drical, barrel-shaped, or inflated spherical cells, which are sometimes thick-walled and 

 always rich in protoplasm. In some species, and especially according to my own 

 observation in Achlya prolifera, these cells may be very large and spherical, unusually 

 full of protoplasm, and abjointed serially and successively at the end of a tube 1 . 

 All such cells may under favourable circumstances in pure water containing free 

 oxygen, and when supplied with suitable food either develope directly into new 

 thallus-tubes or become swarm-sporangia (the resting sporangia of Pringsheim). 

 They are not, as far as we know, characteristic of particular species, but simply 

 resting states which frequently make their appearance under the influence of external 

 causes. 



The deviation in the structure of some oospores from the ordinary type has 

 been described by me at length in another work 2 . It occurs in a few species of 

 Achlya (A. polyandra and A. prolifera), in Dictyuchus clavatus and in an undescribed 

 Saprolegnia, and is not generally characteristic of any of the genera in question. 



Leptomitus lacteus and L. brachynema are imperfectly known forms, belonging 

 probably to the Saprolegnieae, with their thallus-tubes constricted at intervals and 

 with swarm-spores formed in a similar manner to those of Saprolegnia ; with respect 

 to Cornu's genus Rhipidium the author's short preliminary description leaves it 

 uncertain whether its place is here or with the Peronosporeae near Pythium. 



Controverted points. Pringsheim has recently put forth some views which if 

 correct would require a modification to some extent of the account here given of the 

 Saprolegnieae, but only so far as concerns the possibility of a fertilisation of the 

 oospheres by the antheridia. 



Pringsheim claims the office of fertilisation for some small portions of protoplasm 

 with amoeboid movements, which are supposed to make their way through the closed 

 wall of the fertilisation-tube and to pass into the oosphere. Pringsheim has never 

 seen this take place ; he only suspects it on the evidence of some stained preparations, 

 which seemed to show a possible open communication between the protoplasm of 

 the oosphere and that of the antheridium, and of a peculiar phenomenon observed 

 in the antheridia of Achlya racemosa, the account of which must be read in the ori- 

 ginal publication, but which has certainly nothing to do with the process of fertilisation. 

 His observations moreover refer to other species than those specially described above. 

 If there is really an open communication in those species between the protoplasm of the 

 antheridium and oosphere, which, as has been said, is extremely doubtful, we must 

 admit a fertilisation in their case, and in the mode already described in Pythium 



1 \Yalz in Bot. Ztg. 1870, t. IX, Fig. 20; - J5eitr. IV, p. 69. 



