274 THA LL OPHYTES. 



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- 

 legnieae, 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 

 Saprolegnieae 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 

 Pe%i%a confluens ; 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 Saprolegnieae to that already described in the case of Vaucheria 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 CEdogonieae. 



