1915] 



ATKINSON PHYLOGENY IN THE ASCOMYCETES 



357 



child, '97, and others) the cells are uninucleate. The varia- 

 tion in coenocytic character of mycelium probably is due in 

 some measure to the usually fundamental difference between 

 cross wall formation in dividing cells, in the thallophytes and 

 the higher groups of plants, where the fibers of the inner 

 spindle play a part and the cell wall development is centrif- 

 ugal, while in most thallophytes the spindle fibers do not 

 play such a part, wall formation being centripetal, like a clos- 

 ing iris diaphragm. 



The strong plasma connections between the protoplasts of 

 the Laboulbeniales (Thaxter, '96) present a very striking re- 

 semblance to those in the red algae. This feature is regarded 

 by some as very strong evidence of a phylogenetic relation 

 between the Laboulbeniales and the red algae. But intercellu- 

 lar plasma connections are a common feature in all groups of 



plants, 



though 



in many plants these connections are very 



minute. The single central pore in the wall of the Laboul- 

 beniales is perhaps the result of incomplete closing of the ring- 

 forming wall, and in the Laboulbeniales would seem to be of 

 physiological rather than of phylogenetic significance. The 



firm cell walls which are characteristic of the members of this 

 group bear a very definite relation to their habit as external 

 parasites of insects. Standing out free from their bodies and 

 thus having no other means of support than their own rigidity, 

 thick cross walls would interfere with transport of food ma- 

 terial, while the prominent plasma connections permit easy 

 passage of nutrients. 



NOTE VII 



BRIEF OUTLINE OF SOME OF THE THEORIES AS TO THE PHYLOGENY OF THE 



ASCOMYCETES 



I. Descent from the Rhodophyceae. — Sachs ( 74, p. 287) 

 regarded the resemblances between cystocarp and ascocarp 

 as the most important character indicating a relationship be- 

 tween the red algae and sac fungi, although the form of the 

 sexual organs, particularly the carpogonial branch, was also 

 believed to point in the same direction. In his ' Lehrbuch der 

 Botanik' he did not even suggest that the Ascomycetes were 

 derived from the Florideae. The relationships were based 



