1062 Stevens.—-On the Development of the 
of the spores as they lie still connected in the tetrad. It appears that the 
plasma membranes bounding the inner surfaces of the spores now become 
dissolved out in a median plane, so that the spores are free to separate. 
That such disjunction actually soon takes place is shown in Fig. n. 
The processes concerned in the separation of the spores are not entirely 
evident; some observable facts, however, give basis for a conclusion as to the 
main events. By comparison of Figs. 10 and n it is seen that after the 
last meiotic division the vacuole in which a gonotokont was lying increases 
considerably in size, while the young spores just issuing from the tetrad 
decrease in volume. Evidently it is this shrinkage which initiates the 
separation of the spores. In some rare instances thin films of the tapetal 
cytoplasm flow in between the spores before their contraction is far advanced 
(Fig. 12). Prantl, 1 . c., considers the clear space around the spores (seen in 
my Figs. 11 and 12 and his Fig. 77) to be a greatly swollen cell-wall; and 
the delicate strands extending between the spores, as shown in my Fig. 12 
and his Fig. 122, he concludes are planes of differentiation in the swollen 
wall. Evidently the nature of his preparations led him to the wrong 
conception. 
After the spores have separated the plasmodial cytoplasm creeps in and 
completely embeds each one, as shown in Fig. 13 ; and then the spores enter 
upon the final period of growth in size and formation of cell-wall. Figs. 11, 
18, 19, 20, and 21 are drawn to the same scale, and show the progression 
of these events as the spores advance to maturity. Figs. 18 and 19 were 
taken from the sporangial stage shown in Fig. 13. Here the wall of the 
spore has begun to thicken ; and, whereas with the triple stain, safranin, 
gentian-violet, and orange G, it was when first formed stained purple, it now 
is stained red. At this stage the sculpturings on the surface of the wall 
characteristic of this species (shown in Fig. 21) have not yet appeared. 
Fig. 19 is a surface view giving the three flattened surfaces where the other 
three spores of the tetrad joined it. There is a line of cleavage down each 
of the three angles, one of which is seen in cross-section in Fig. 18. Even 
in these immature spores one often finds in his preparations the three flaps 
parted and revealing the nucleus within. 
The wall now thickens, heaping up ridges at its outer surface and adding 
an inner layer which comes out almost colourless from the triple stain 
(Fig. 20). The inner coat (endospore, or intine) is not continuous at the 
three angles, as shown in cross-section through one of the angles in Fig. 20, 
neither does it follow the protruding lips of the outer coat (exospore, or 
extine) at this place, as Beer (’ 06 ) finds to be the case in Helmintkostackys . 
When the spore is of the age shown in Fig. 18 a thin film of cytoplasm 
can be followed out from the mass which holds the nucleus embedded, 
around the inside of the wall; but when the spores have arrived at the stage 
shown in Fig. 20 the entire protoplast seems to have receded to one corner 
