230 Barker . — The Morphology and Development of 
little is known of the cytological behaviour in the latter 
leading up to spore-formation. Wager (25) has shown that 
five to eight nuclei are present in the zoosporangia of Albugo 
Candida , when those bodies are cut off by a wall from the 
sporangiophore. Each nucleus remains undivided and becomes 
the nucleus of a zoospore, which bodies are formed according 
to Biisgen (4) by the simultaneous division of the protoplasm 
into several distinct portions. This process is thus far removed 
from that occurring in typical asci. But the ascus must be 
regarded either as a specialized sporangium or as an entirely 
new structure without any homologues : and it has been seen 
that a method of spore-formation, which may be looked upon 
as approaching that found in asci, occurs in the oogonium of 
Albugo , and that the latter organ is probably a derivative of 
a gametangium. The balance of probability thus seems to 
rest with the view that the ascus and the zoosporangium are 
homologous. Moreover, Harper’s results have been obtained 
from typical highly evolved asci and sporangia, and it is 
hardly to be expected that such diverse and characteristic 
structures would exhibit signs of a common origin, as might 
be obtained from more primitive forms. Ikeno’s studies on 
Taphrina (14) show that the method of spore-formation in the 
asci of that genus is very different from Harper’s typical 
method. 
Apart, however, from the difficulty of the manner of cell- 
division there is another obstacle against the acceptance of 
these homologies. It arises from the behaviour of the nuclei 
in connexion with the formation of a typical ascus. The 
typical ascus is formed by the cutting off of a penultimate 
cell from an ascogenous hypha containing two nuclei which 
fuse together, leaving the young ascus uninucleate. The ascus 
speedily becomes multinucleate by repeated divisions of the 
fusion-nucleus, and each of the last formed daughter-nuclei 
becomes the nucleus of an ascospore. In the Oomycetes the 
antheridia, oogonia and zoosporangia are multinucleate from 
the moment of formation, and the nuclei in the latter structures 
become without any division the nuclei of the zoospores. 
