274 
THALLOPHYTES. 
oospheres, considerable contraction taking place. At the same time the antheridia 
are also formed, appearing as much slenderer lateral branches, beneath the oogonia 
but sometimes above their basal wall. These antheridial branches are usually much 
curved; their upper portion is separated by a septum, and the terminal cell thus formed; 
the antheridium usually applies itself firmly to the surface of the wall of the oogonium. 
The process of fertilisation itself, which had previously been only imperfectly known, 
presents, according to the most recent observations of Pringsheim, several remarkable 
peculiarities which throw considerable light on the genetic relationships of the Sapro- 
legnieee, and on the essential nature of the various modes in which it takes place. 
Even before the contents of the oogonium have broken up into oospheres, a larger 
or smaller number of spots of a lighter colour (Fig. 179, C) may be observed on the 
oogonium ; at these spots Pringsheim states that the inner layer of the cell-wall protrudes 
in the form of a wart to form the conjugating organ by which fertilisation is subsequently 
effected ; in some species of Saprolegnia and Achlya these warts remain covered by the 
outer layer of the cell-wall of the oogonium. As soon as an antheridial cell becomes 
closely applied to the oogonium, a protuberance of the inner layer of the cell-wall 
of the antheridium first of all penetrates into the outer layer of the cell-wall of 
the oogonium, and meets the wart already described belonging to the inner layer ; 
this latter is then absorbed at the point of contact, and the protuberance of the 
antheridium grows into a narrow tube which penetrates deeply into the oogonium, its 
extremity burying itself in the midst of the oospheres. These processes are only par- 
tially represented in Fig. 179, which was drawn long before the discovery of the actual 
phenomena. According to Pringsheim the extremity of the fertilising tube opens in the 
interior of the oogonium ; extremely minute bodies are repeatedly expelled in jerks 
and after long intervals, which are seen among the oospheres, and which are probably 
antherozoids or bodies with a similar function. But the substance expelled from a single 
fertilising tube may serve for the impregnation of several oosphores in an oogonium ; and 
it is the more probable that this takes place since the number of these tubes which pene- 
trate into an oogonium is usually different from that of the fertilised oospheres. With 
regard to the bright spots in the wall of the oogonium, through which, as we have 
seen, the fertilising tubes enter, it is evident that a process takes place here similar in 
its nature to conjugation, since not only does the antheridium grow into the oogonium, 
but the inner layer of the wall of the oogonium also, so to speak, grows towards the 
antheridium by the formation of the wart already described, in order to unite with 
it, although no actual coalescence of the contents takes place at that time, the wart 
being subsequently penetrated by the fertilising antheridial tube. But in some 
Saprolegniese the formation of this conjugating wart proceeds further ; it penetrates 
through the outer layer of the wall of the oogonium, opens at the surface, and 
each wart thus becomes an orifice through which the antheridial tubes penetrate : 
sometimes, according to Pringsheim, the conjugating warts become raised above the 
spherical surface of the oogonium in the form of more or less elevated protuberances, 
or even grow into tolerably long tubes, the apices of which are occasionally met with in 
conjugation with an antheridial tube. These cases, although rare, manifest still more 
strikingly a certain resemblance to the conjugation of the Zygomycetes, and perhaps 
a still closer analogy to the process of fertilisation in some Ascomycetes, such as 
Pezi%a conßuens ; or a comparison might even be drawn between the trichogyne of 
Nemalion and the protuberances of the oogonium. The similarity of the process of 
fertilisation in the Saprolegniese to that already described in the case of Faucheria is 
sufficiently clear; that spot in the oogonium of Vaucheria which subsequently opens and 
exudes a drop of mucilage may obviously be compared with the conjugating wart in those 
oogonia which contain only a single oosphere ; only that in Vaucheria no fertilising 
tube is usually developed from the antheridium, since the antherozoids are larger, and 
remain motile for a considerable period, finding their own way into the open oogonium. 
Pringsheim has already pointed out the corresponding analogy with the CEdogoniese. 
