Zoogonidia 



389 



anterior pole, which is colourless and sometimes extended to form a pro- 

 tuberance, there is a circle of numerous short cilia. This unique zoogonidium 

 sometimes possesses a pigment- spot. Its exit from the mother-cell only 

 occupies a few minutes, since the rapid disappearance of the delicate vesicle 

 enables it to swim quickly away. On coming to rest it attaches itself by its 

 anterior hyaline end, loses its cilia and develops a cell-wall. From this point 

 onwards germination conforms to two very distinct types, although in both 

 types the cell formed directly from the zoogonidium remains as a differentiated 

 basal cell. 



Freund has stated that zoogouidia can be produced in CEdogonium pluviale by trans- 

 ferring the filaments from a cane-sugar solution to dilute Knop's solution. They are often 

 formed in numbers in both the spring and the autumn when CEdogonium- -filaments are 

 brought from outside temperatures to the temperature of the laboratory. 



Fig. 243. Formation and escape of the zoogonidium in (Edogonium 

 concatenatum (Hass.) Wittr. x 27f> (after Him). 



Iii the first and most usual type of germination the fixed end of the cell 

 puts out an organ of attachment, which may be simple (fig. 244) or branched 

 (fig. 245 A, and E H). The nature of this hapteron depends to a great 

 extent upon the particular species and so also does the degree of tumidity of 

 the cell. In most species the basal cell is more or less tumid, but in a few it 

 remains almost cylindrical. The hapteron is in some cases an attaching disc 

 and in others a simple or branched rhizoid. The protoplast extends into the 

 rhizoid and its branches, but as a general rule the chlorophyll does not. The 

 disc-development is generally in those young plants which are attached to 

 a definite substratum (fig. 244 D, E and H), whereas when the young plants 

 remain free-floating and unattached the rhizoidal development is usually 

 most pronounced, and often only a single unbranched rhizoid is developed 

 (fig. 244 F, G and /). This unicellular plant has a distinct apical cap, often 

 convex or conical, and sometimes furnished with an apiculus. 



