336 Blackman . — On the Fertilization , Alternation of 
layer of very finely granular cytoplasm with apparently no reserve-material, 
and the whole is enclosed in a very thin cell-wall. 
The spermatia make their escape through the ostiole, and are found 
spread out on the leaf in the immediate neighbourhood. They took no 
part in aecidium-formation or in any other process, and numbers of them 
when observed on the leaf-surface appear to be in a disorganized state, 
in which the distinction between nucleus and cytoplasm is almost 
completely lost. 
Gymnosporangium clavariaeforme. 
The mycelium in the leaves of the Hawthorn which bears the 
spermogonia shows clearly the single nuclei apparently always enclosed 
in separate cells. They are of small size, and usually show no distinct 
nucleolus, and their nuclear membrane is often indistinct. The spermogonia 
appear very early after infection, in about seven to ten days. 
The spermogonia are flask-shaped structures of the usual type, and 
are developed beneath the epidermis. They arise from a layer of small- 
celled ‘tissue’ (plectenchyme), which gives origin to a number of upwardly 
directed and parallel hyphae, the spermatial hyphae. Certain of these 
hyphae, chiefly the peripheral ones, grow out to form the paraphyses which 
project through the ruptured epidermis. The others bud off each a series 
of spermatia, which collect in the cavity of the flask, and later become 
extruded (Fig. 48). 
This form is a favourable object for studying the exact development 
of the spermatia. The spermatial hyphae are narrow, elongated cells with 
a central elongated nucleus, which shows a granular chromatin network 
and one or more small nucleoli ; the nuclear membrane, however, is 
indistinct (Fig. 49). The hypha contains only finely granular cytoplasm. 
It is furnished at the free end with a curious ring of thickening, which 
is easily rendered visible by the fact that it takes the Congo-red with more 
avidity than the rest of the cell- wall (Figs. 49-54). 
The first beginning of the development of a spermatium is the pushing 
out of a finger-like projection from the free end of the hypha, thus 
displacing the last-formed spermatium (Fig. 49). This projection contains 
exceedingly finely granular protoplasm. When it has attained its full size, 
or a little earlier, the nucleus of the spermatial hypha begins to undergo 
a process of condensation (Fig. 50), so that it is transformed into 
a homogeneous and deeply staining chromatin mass (Figs. 51 and 55), 
the nucleolus or nucleoli being apparently squeezed out into the general 
cytoplasm (Fig. 55 a). The condensation of the nucleus may begin at one 
end and progress downward, as shown in Fig. 50. The mass of chromatin 
then becomes drawn apart into two masses (Figs. 52, 56), which remain 
