[Vol.. 2 



318 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



comycetes he was led to the conclusion that the Ascornycetes 

 were derived from the Phycomycetes. This doctrine is based 

 chiefly on the evidence of a phyletic relation between the sex- 

 ual organs of the two groups. In spite of the persistence of 

 the belief in the origin of the sac fungi from the red algae, 

 deBary's doctrine of their descent from the Phycomycetes has 

 had many adherents. Nowhere in deBary's writings have I 

 been able to find any statement which can be construed as 

 favoring the origin of the sac fungi from the red algae. The 

 esteem in which his judgment is held, even at the present day, 

 has led to the republication of a rumor of an ante mortem 

 statement by deBary to the effect that he was inclined to the 

 view that the procarps of the two groups pointed to the origin 

 of the Ascornycetes from the Rhodophyceae! 



Our present knowledge of the cytology of the ascus would 

 not perhaps favor such close contact between the Ascornycetes 

 and Phycomycetes as would appear from the knowledge pos- 

 sessed in deBary's time. Unfortunately we are not yet in 

 possession of any cytological knowledge of spore production 

 in the zygote of the Phycomycetes which we can use for com- 

 parison. But at any rate, the difficulties in this relation are no 

 greater than are met with in attempting to derive the ascus 

 from the carpospore or tetrasporangium of the red algae. 



Origin of the ascogenous threads. — The ascogenous threads 

 are outgrowths of the zygote or oogonium and represent one 

 method of splitting up and proliferation of the same in accord- 

 ance with recognized principles of progression in the same 

 direction of increase in the output of spores following the 

 sexual process, or its equivalent, and terminating the diploid 

 phase. 



One of the most instructive forms suggesting a mode of 

 transition from the Phycomycetes to the Ascornycetes, is Dipo- 

 dascus. Its sexual organs are strikingly like those of certain 

 Mucorales or Peronosporales in their young stages. The 

 sexual organs, which can be recognized as antheridium and 

 oogonium, arise either from adjacent cells of the same thread, 

 or from different threads. After resorption of the wall at 

 the point of contact, the fertilized oogonium (or zygote) grows 



