364 OEGANOGRAPHY. 



ring becomes detaclied from the stalk at one end, straightens, 

 and appears as a long mucilaginotis cord protruding from the 

 sporocarp {fig. 793, p), and bearing on its sides somewhat oblong 

 spikes of fructification {fig. 793,/). These spikes are at first 

 enveloped in a membrane, and are composed of two distinct or- 

 gans, called antheridia, and ])istillidia sporangia or ovules. These 

 organs are attached to a sort of placenta, the antheridia being 

 on one side, and the sporangia on the other. 



Each sporangium contains but one spore. It consists of a 

 central nucleus, surrounded by a cellular coating except at 

 its apex, where there is a little cavity {fig. 795). According to 

 Hofmeister, " this cavity is gradually filled up with cellular 

 tissue, constituting a conical prothallium confluent with the 

 nucleus. A single archegonium is formed in the centre, the 

 orifice of which coi*responds with the apex of the prothallium." 

 In this an embryo is ultimately formed, which, when it germinates, 

 gives off a frond in one direction and a root in that opposite to it. 



The antheridia contain a number of small cells {fig. 794), 

 which ultimately develop long spiral spermatozoids. These 

 small cells are sometimes called pollen-spores or small spores, 

 while the large germinating spore is called the ovulary -spore or 

 large spore. 



Fig. 796. Fig. 797. 



Fig. 796. Transverse section of the sporocarp or spore-fruit of Pilularia 

 globulifera. After Henfrey. Fig. 797. Vertical section of the sporo- 

 carp of Salvinia, showing sporangia iu one cavity, b, and antheridia in 

 the other cavity, a. 



In Piltdaria, the fructification consists of stalked, pill-shaped, 

 hairy sporocarps. The interior of each sporocarp is divided 

 usually into four cells {fig. 796), and when ripe it opens by four 

 valves. In the interior of each cell there is a mucilaginous pro- 

 cess or placenta attached to the walls, upon which are placed 

 numerous antheridia and sporangia or ovules, as in Marsilea. 

 The structure of these antheridia and sporangia resembles in all 

 essential particulars those of Marsilea. In fact, the only differ- 

 ence between the fructification of Marsilea and Pilularia, is the 

 more complicated nature of the sporocarps in Marsilea, 



