KEPRODUCTIVB CELLS. 151 



Fertilisation consists in the fusion of an antherozooid with an 

 egg-cell, the nuclei of both participating in this fusion; as a rule, 

 a large number of antherozooids may be seen swimming round 

 one of the spheroidal egg-cells, but only one motile cell is needed 

 for the purpose of fertilisation (see Fig. 109, 6). 



After fusion, the fertilised egg-cell (oospore proper) is divided 

 by two walls into four cells, and subsequent divisions result in 

 the formation of a pear-shaped structure which, after a time, 

 becomes fixed by a branching "foot" at one extremity to a 

 suitable support. The foot does not function as a root, or 

 absorbing organ, but only as a means of attachment. 



(c) Eeproduction in Vancheria (see Fig. 110, 1, 2, 3, and 4). 



The reproduction of Vuiicheria by means of swarmspores has 

 already been studied. The other method ik a sexual one in 



Fig. 109.— Repkoductiox in Fucus reticidotus (Diagb.mimatic). — 1. Sec- 

 tion across a female coneeptacle showing oogonia springing from the 

 bottom of it and ^numerous paraphyses. 2. A single oogonium, com- 

 posed of a basal cell and an oogonium proper, m liich contains the 

 oosphere. 3. Division of the oosphere into eight egg-cclls previous to 

 fertilisation. 4. An antheridial " branch " from a male coneeptacle ; 

 the antheridia spring from the end and sides near the top of the 

 "branch." The antheridia contain tljo mother-colls of the anthero- 

 zooids. 5. A single antherozooid, with lateral eyc-Hjiot and two 

 vibratile cilia situated laterally. C. An egg-uell, freed from the 

 oogonium and surrounded by antherozooifls ; one of these will 

 ultimately fuse with the cytoplasm of the egg-cell, the nuclei also 

 fusing. 



which the antherozooid and the oosphere form the effective cells. 

 An antheridium and an oogonium arise on the same filament 

 close to one another, by the formation of protrusions of the cell- 

 wall into which a certain amount of cytoplasm fluws with nuclei 

 and chloroplasts. The antheridium is a small (.■ui\ed .structure, 

 and the apical part becomes cut off from the lower portion by a 

 thin partition-wall. In this apical part the cytoplasm and 

 nuclei are soon differentiated into a number of ciliated anthero- 

 zooids, these being somewhat similar in structure to the anthero- 

 zooids of Fucus. The oogonium arises close to an antheridium 

 m a similar manner to the latter, by the cutting off of the pro- 

 trusion from the main filament by a thin partition-wall ■ the 

 cytoplasmic contents of this protrusion form the oosphere. 



