THALLOPHYTES. 7 



Vaucheria and many Saprolegnieae, or it developes from its cell-contents a few or 

 .many swarm -cells, each of which ultimately gives rise to a plant like the mother-plant, 

 as in Sphaeroplea, Oedogonmm, and Cyst opus. 



A transition from the formation of zygospores to that of oospores is also to be 

 found in the conjugation of non-motile gametes ; indications of it occur in the Con- 

 jugatae, a section of Algae ; but distinct formation of oospores in this manner has 

 hitherto been certainly ascertained only in some Fungi, the Peronosporeae (as regards 

 the Saprolegniae rid. infra). One or more oospheres are formed in a cell which 

 dilates and becomes globular, the oogonium. Close to it grows another branch of the 

 thallus, at the extremity of which a cell is divided off by a septum to form an anthe- 

 ridium. This cell thrusts a tube, the fertilisation-tube, through the wall of the oogonium 



FIG. 4. Formation of oospores in two species of Peronosporeae (/ VI Pythium gracile, VII Peronospora. 

 arborescens) ; in both cases the oogonium swollen into a spherical shape contains only a single oosphere, 

 which is fertilised in VI and VII and forms the oospore invested with a cell-wall. After De Bary. 



as far as the oosphere, and from the opened tube protoplasmic matter issues, which 

 mingles with the substance of the oosphere. Here there are no spermatozoids ; the 

 process is closely allied to that of the formation of zygospores by union of non-motile 

 gametes. 



3. Formation of Fructifications producing Spores (' sporocarps ') from 

 procarps and archicarps (carpogonia). 



a. FERTILISATION OF PROCARPS IN THE FLORIDEAE. The male elements are small 

 cells without active motion, and are known as spermatia. The female organ, the 

 procarp, consists before fertilisation of two parts : an apparatus for the reception and 

 transmission of the male fertilising substance, which apparatus disappears after fer- 

 tilisation has been accomplished, and a part which is excited by fertilisation to a 

 process of growth which results in the fructification which produces the spores. This 

 second portion of the procarp is called the carpogone ; the cells which compose it, 

 and which are not unfrequently separated by barren cells, are the carpogcnous cells. 

 The receptive apparatus is called the trichogyne. 



The simplest form of fertilisation of procarps, apart from the non-motile condition 

 of the spermatia, resembles the processes in the fertilisation of the oogonia of Oedo- 

 gonium, Coleochattf, and their allies. , It is exemplified in the Bangieae, where 



