Harper. — Cell- Division in Sporangia and Asci. 519 
plasma- membrane of the surface or of vacuoles. This appears 
to be a very fundamental distinction. It may, however, be 
taken as indicating possibly a further resemblance between 
the plasma-membrane and the fibres of the karyokinetic 
figure. 
If we consider now the bearing of the observations pre- 
sented, on the doctrine that the ascus is a more highly 
developed and specialized modification of the sporangium 
of the Zygomycetes, it is plain that the very different 
methods of cleavage in the two cases are opposed to the 
assumption of any close relationship between them. In fact, 
it seems rather difficult to imagine any intermediate stages 
which could connect the process of cleavage by surface- 
furrows, as seen in the sporangium, with the free cell-formation 
of the ascus. It must be noted too that Popta’s work on 
Ascoidea and Protomyces, which Brefeld considers intermediate 
forms between the lower Fungi and the Ascomycetes, has 
failed in any way to bridge this gap. Until some transitional 
forms have been found between these widely separated 
methods of cell-division, their evidence must be considered 
as decidedly against the assumption of any morphological 
relationship between the sporangium and the ascus. The 
method of division in the sporangium by surface-furrows is 
easily connected with other cases of division by constriction, 
such as are seen in the cell-division of Cladophora or in the 
formation of the conidia in the Erysipheae as I have described 
it, but the free cell-formation in the ascus seems as yet 
entirely unique, and its occurrence in widely separated forms 
of the Ascomycetes is justification for considering it as 
perhaps the most important and specific feature by which 
to distinguish the ascus from other spore-producing cells. 
The presence of epiplasm has always been considered one 
of the most distinctive features of the ascus, and those who 
have contended for the relationship of the sporangium and 
ascus have been much concerned to discover a similarity 
between the epiplasm and the intersporal slime in the spo- 
rangium. It is, however, sufficiently apparent that these two 
