82 DIVISION I.—GENERAL MORPHOLOGY. 
and exceptional cases the release of the ripe spores is left to chance, there being no 
special arrangement made for it, and the spores may even germinate inside the mother- 
cell, the germ-tubes piercing or bursting through its wall, as may be seen in the 
sporangioles of Thamnidium and its allies. 
The arrangements for the escape of the spores vary in different species. 
a. The aquatic swarm-spores of the Saprolegnieae (with one partial exception to 
be noticed hereafter), of the Peronosporeae and Chytridieae make their exit through 
a narrow orifice, formed usually at the apex of the wall of the mother-cell by the sudden 
swelling and disappearance of a circumscribed portion of the wall of the mature 
sporangium. The spot is marked out in many species by gelatinous thickening 
of the membrane before it begins to swell. This is nowhere more conspicuous than 
in the sporangia of Phytophthora, in some species of Peronospora, and in some of the 
Chytridieae which have gelatinously thickened terminal papillae; in other cases, as 
Saprolegnia, the thickening has not been observed. While the place of exit swells, 
the entire contents of the sporangium, the mass of spores and the surrounding matter, 
absorb water and also swell!; and as the lateral walls of the sporangium are but 
slightly extensible, the spores which lie beneath the place of exit are first squeezed 
out through it and the others follow. 
rf The proceeding may vary in individual 
Qs ‘a cases, and it remains for investigation 
f to determine to what extent the spores 
@ themselves, the intermediate parting 
substance (see p. 74) and perhaps also 
an inner layer of the wall of the spor- 
angium, participate in the first general 
ie, pttors nn swelling caused by the absorption of 
See rae erence moin: <eesnecome water, In the cases which have been 
more carefully examined (Achlya, Sap- 
rolegnia and Phytophthora, Fig. 42) it can be seen directly that it is the hyaline substance 
surrounding the spores inside the firm wall which swells the most. Itis also observed 
in most cases that a hyaline layer on the inner surface of the firm wall first comes 
into prominence, and increases in breadth and pushes the mass of spores towards the 
middle of the sporangium and the place of exit. The spores, even where as in some 
cases they show independent movements before they are set at liberty, are now 
virtually passive, and in Achlya especially they are evidently squeezed together as 
they escape from the sporangium by the limpid mass which surrounds them. It is 
therefore in the swelling of this mass that the expelling force resides ; but it is still 
uncertain whether the mass consists entirely of the original soft partition-layers which 
must in that case suffer partial dislocation when the spores are discharged, or whether 
an innermost layer of the wall of the sporangium swells and some product from the 
spores themselves is also added. 
The phenomena connected with this swelling at the place of exit occur only at 
a given moment after the formation of the spores is completed, and in water more- 
over which is perfectly pure and contains free oxygen. That the point of exit, which 



1 Walz, Bot. Ztg. 1870, p. 689. 
