On the Morphology and Development of Phoma Richardiae n. sp. 
251 
led me to the belief that the spores were not formed by a process of 
budding, but by division and rounding off of the wall cells. Examination 
of a larger number of young pycnidia, however, disposed of this idea, 
since several were found in which spores in the process of budding off 
were discovered (Fig. 2, j>— 5 ). Here and there spores which appear 
bicellular are occasionally found in a young pycnidium (Fig. 2, j). I have 
never seen this in a pycnidium which has reached any considerable degree 
of development, and only once or twice in very young pycnidia. 
In discussing the changes which the wall surrounding the spore 
cavity undergoes during growth, it may be noted in the first place that 
it -expands greatly, and that the number of cell layers of which it is 
composed, diminishes (comp. Fig. 2, 2 with 8 , p). Expansion might be 
brought about by division of the cells, by rearrangement, or by a combi¬ 
nation of the two methods. But cell division alone could not lead to a 
thinning of the wall. A certain amount of separation and rearrangement 
of the cells must go on, and they must be comparatively loosely bound 
together to allow of this process — a view which is rendered all the 
more tenable by the fact that the tissue-like mass owes its origin to the 
interweaving of hyphae. The wall is best regarded, therefore, as a more 
or less mobile aggregation of cells; not, as it appears in section, as a 
firm pseudoparenchyma. The production of a spore cavity in the once 
solid mass, and of a mouth in the once continuous wall, is no doubt 
referable to this mobility of the cells. There is no sign of disorganisation 
of the cells in either case, nor, in the latter case, of tearing such as 
occurs in the formation of some pycnidia mouths. Here the mouth is 
formed gradually, and, like the spore cavity, opens wider as growth 
proceeds (Fig. 2, 7 —p). This is precisely what would occur if it owed 
its origin to separation of the cells. In some cases formation may be 
assisted by the presence of the packed spores in the cavity; but the 
mouth is often formed before the accumulation of spores within is very 
dense (Fig. 2, 7 ). 
Mere rearrangement of the cells, however, could not account for 
such a great expansion of the wall as occurs (comp. Fig. 2, 2 and p). 
New cells must be added. Now it was observed in tracing the early 
evolution in moist-chamber cultures, that the central mass continually 
adds to its bulk during growth, by the absorption of hyphae from the 
outside. No doubt this process accounts, in part at least, for wall expansion. 
Either hyphae from the outside push in between the already existing cells, 
or, what amounts to the same thing, the primary cells push outwards, 
gradually enclosing peripheral hyphae among themselves. 
The irregular size and shape of the wall cells and the fact 
that, as the pycnidium ripens, they become flattened, make it difficult 
to compare them in different stages of growth. Flattening, however, 
seems to take place chiefly late in life (comp. Fig. 2, 7 , 8 and p) and 
comparison of Fig. 2, 1—8 shows that the cells do, on the whole, become 
smaller as development proceeds. It is probable therefore that the process 
of cell division which assists in the formation of the primordium in some 
cases, is instrumental at a later period in aiding wall expansion. 
The meristogen pycnidia are produced in too small numbers and are 
too much intermingled with symphyogen to make the task of picking 
them out separately and trying to follow their evolution in the later stages, 
