Harper . — Cell- Division in Sporangia and Asci. 489 
3. Embryonic development, in which the spores increase in 
size and become multinucleated. 
4. Ripening, in which a protective wall is formed about the 
spore and the protoplasm passes into a denser resting condition 
with abundant inclusions of reserve food -materials. 
5. Germination, which is a mere continuation of embryonic 
development by which a sporangium produces a number 
of embryos (swarm-spores). 
A mechanical explanation of the cleavage I have just 
described is by no means easy. The formation of superficial 
constriction-furrows cutting into the protoplasm is analogous 
to what is seen in the division of the animal cell especially,, 
as noted above, to the phenomena of cleavage of certain insect 
eggs. Heidenhain 1 and later Kostanecki 2 have attempted to 
refer the constriction which divides the animal cell to the 
contraction of fibres arranged about a centrosome. Such sets 
of fibres are certainly not concerned in the division of the 
Synchitrium sporangium. The gradual cleavage, first into 
large multinucleated segments and only later into uninucleated 
spores, which are formed in 5 . Taraxaci, could not well be 
referred to any such simple systems of contractile fibres as 
the above-named authors discuss. 
The decrease in volume of the protoplasm during the 
process might suggest that the cleavage is connected with the 
loss of water, and the formation of superficial furrows might 
be compared to the cracking of the surface of a drying mass 
of a colloidal substance. Such an explanation however in 
itself alone is entirely inadequate to explain the definiteness 
and certainty with which the final result of the cleavage is 
attained. The nuclei are seen to be the centres of the 
ultimately formed segments, which would by no means 
necessarily be the case as a result of simple cleavage by 
drying. We might indeed assume that the loss of water was 
least in the neighbourhood of the nuclei, which would meet 
the demands of the case without however simplifying the 
1 Archiv fur Mikr. Anat. 1894, P* 4 2 3« 
2 Ibid. 1897, p. 651. 
