174 THE SAPROLEGNIACEAE 



2-ceIIed stalk very like the oogonia of our plant. The sporangia are 

 also like the majority in ours and not all spherical; some are oval. He 

 did not see the spores escape or swim, but he shows no spores at tips of 

 sporangia and several sporangia are drawn with one or more retained inside. 

 He says that about six are formed. He shows several sporangia (as many 

 as four) in a close group by budding below as in ours, and as many as 

 three in a row in one case. His figures are so nearly like ours that we 

 must let our plant go as /I. brachynema. Pringsheim, it is true (1. c, p. 

 289), says that in this species he has observed that the spores are formed 

 not as in Saprolegnia but as in Achlya. Tiesenhausen 's description and 

 figure of the variety major represent our plant well, but as his variety 

 is based on size of threads and sporangia and as our plant connects 

 these sizes up with those of the type it is probable that this variety is 

 only a form. 



Zopf's good description and figures of A. pyrifera clearly exclude 

 our plant on two main points. In the former the majority of the oogonia 

 are borne on the tips of main threads, others not so borne are either 

 sessile on the side of main hyphae or with a single short stalk cell. The 

 spores are described as encysting, as a rule, in a group at the sporan- 

 gium mouth, or less often swarming at once on emerging. In the latter 

 the oogonia are nearly all borne on rather short lateral, more or less 

 moniliform branches composed of a few short segments. A culture 

 shows a peripheral series of sporangia with the oogonia forming in much 

 larger numbers on laterals from the same hyphae nearer the substratum. 

 Spherical sporangia may be distinguished from young oogonia before 

 the spore initials appear by the longer and clearer cell below them. 



Minden's species, A. punctata, is more than doubtful. He separates 

 it only on the punctate membrane of the resting spore (oogonium); but, so 

 far as his figures show, this punctation is nothing more than the emul- 

 sified contents of the young oogonium, a condition shown also by Zopf 

 for A. pyrifera. 



The spherical resting bodies called by Zopf " Dauersporen" or gem- 

 mae are, we believe, oogonia both in his plant and in ours. Tiesenhausen 

 comes to the same conclusion for /I. pyrifera (1. c, p. 298). We know of 

 no gemmae in this or related groups which have thick walls and undergo 

 a maturation within like an egg. Moreover, as shown below, there is 

 good reason to believe that fertilization occurs. 



Observations of threads on a corn meal agar plate show that the 

 suboogonial cells reach their final size before the young oogonium ap- 

 pears. The oogonium appears as a very small globular tip on the end 

 of the distal stalk cell. The protoplasm can be seen passing from the 

 hyphal segment through the rounded stalk cells into the growing oogo- 



