236 Campbell \ — -On the development 
The Microspores and Male Prothallium. 
The spores are of the tetrahedral type, and the vertical 
diameter is considerably less than the transverse. The three 
radiating ridges where the spore was formerly in contact with 
the other members of the tetrad are very prominent, and mark 
the place where the episporium and exosporium rupture when 
the antheridium is mature. 
Arcangeli 1 succeeded in demonstrating the presence of a 
vegetative cell of the prothallium, but beyond this his obser- 
vations were very incomplete, owing to the fact that he did 
not succeed in freeing the prothallium from the exosporium, but 
simply rendered the latter as transparent as possible. It is, 
however, possible to remove the exosporium entirely, and when 
this is done it is found that we have to do with a much more 
complicated structure than was supposed, and one whose 
development can be followed with a precision that is quite 
out of the question when the observations are hindered by 
the semi-opaque exosporium, which absolutely prevents a clear 
view of the interior of the spore, even when every available 
means is used to render it transparent. The spore contains 
much starch, and in the later stages it is sufficient to place 
the spores in a drop of water upon a glass slide and cover 
them with a cover-glass, and heat the slide over a flame 
until the water boils, when it will be found that the starch 
swells up sufficiently to rupture the outer coats of the spore 
and force out the young prothallium, surrounded only by the 
perfectly transparent endosporium. The prothallium is in no 
degree injured by this process and the dissolution of the 
starch is rather an advantage, as the cell-walls and nuclei are 
more easily studied than when the cells are filled with the 
opaque starch-granules. 
In the earlier stages this simple process is not sufficient, 
and it is necessary to employ caustic potash in order to 
free the prothallium from the exosporium, but a very small 
amount must be used, and it must afterwards be thoroughly 
1 l.c., p. 339- 
