Mabch 1, 1898.] 



KNOWLEDGE 



55 



thus produced aet free an antluTozohl. This is a free- 

 swimming body with two ciha, similar to the zoogonidia, 

 but smaller, and it reaches and fertilizes the oosphere by 

 different methods in the various species. In the common 

 British species it appears that any cell of the disc may 

 enlarge and become an oogonium ; and, similarly, other 

 cells may divide and become antheridia, though often on 

 separate plants. The fertilization of the oospherea by 

 the antherozoids in these cases apparently takes place by 

 the passage of the latter through an opening in the cell 

 wall of the oogonium. 



The process has been studied in detail by Pringsheim in 

 the case of a species which is not found in this country — 

 Coh'ochat,- /nihinntd (A. Br.) — and in this case the highest 

 degree of specialization seems to be reached. The species 

 is one of those already referred to as having a half-fila- 



function to the sti/U of a flower, and is a special structure 

 developed in connection with the process of fertilization. 

 Its presence in this one type of fresh-water weed is specially 

 interesting, because it is a characteristic organ in the case 

 of the red seaweeds, though in these the fertilizing agents 

 are non-motile bodies or pollinoids. 



This similarity between the reproductive process in 

 Coleochivte and in the red seaweeds is still more marked in 

 the subsequent stages. After fertilization not only does 

 the oosphere enlarge and become surrounded by a cellulose 

 wall (constituting an oospore or oosperm), but some 

 physiological influence extends to the adjacent cells, causing 

 them to divide and grow up round it, enclosing it in a 

 protective cellular layer or perirarp. 



The structure thus formed— which has been called by 

 different authors a ciirpoijonium or spermocarp — is therefore 



A — Young plant of Cohochcefe sciifafa (Brcb), magnified about one hundred times. In the upper part some of the 

 cells are dividing into four previous to the development of antherozoids. B. — A fertile filament of C. puleinafa (A. Br.), 

 showing the oosphere enclosed in the oogonium with its trichogyne {t). Below are the antheridia {a) and above an 

 antherozoid (a') . c. — An oogonium in same species after fertilization, showing the surrounding pericarp (p). d, — The 

 spermocarp liberating its carpospores. E. — Zoospores formed from the earpospores. (b to E, after Pringsheim.) 



mentous, tufted growth, and here the oogonia are terminal 

 on the ends of the threads. 



The oogonium is, as before, only an enlarged 'and 

 specialized cell containing a single oosphere, but its wall 

 is prolonged into a long tubular projection termed a 

 " trichogijiu." Antheridia are developed from adjacent 

 cells in this species, but in some other cases on separate 

 plants. 



There is no doubt that the trichogyne corresponds in 



* The species is not uncommon in the lake* of Central Europe. 

 I am indebted to Prof. Oltmanns for caUing my attention to it on 

 plants of IsoHes in the Titisee, near Freiburg-in-Baden. 



a very mnch higher type of fruit than the simple oospore 

 of Viiuclieria. 



The fruit remains quiescent during the winter, but in 

 the next spring the oospore divides and forms several cells 

 or citrpoapoi-es : it does not itself grow into a new Cohochcete 

 plant. Fm-ther, the carpospores themselves do not grow 

 mto new vegetative plants. They liberate free-swimming 

 zoospores, and these in their turn give rise to new (.'oho- 

 chceif plants which may reproduce themselves again by 

 either method. 



WhUe, then, an ordinary sterile plant of CoL-ochate does 

 not show us any particular advance in general structure 

 from many of the lower ThiiUophijta, there are certain well- 



