Vaucheriacece 109 



them have even reached a high stage of specialization, having 

 developed organs analogous to the stem, leaf and root of higher 

 plants. In the genus Caulerpa the cell is strengthened by trabe- 

 culse which traverse the lumen of the cell from wall to wall. 



Asexual reproduction takes place by proliferous shoots, by 

 non-ciliated spores and by zoogonidia. In most of the Siphonese 

 numerous zoogonidia arise in a zoogonidangium, but in Vaucheria 

 only one large one is produced. 



The plants are generally attached by strongly developed haptera. 



The only family of the order which inhabits fresh waters is the 

 Vaucheriaceae, and it is also the only family in which well- 

 differentiated sexual organs occur. The tropical family Phyllo- 

 siphonaceae includes a number of Algae which live as parasites on 

 the leaves of Phanerogams. 



Family 1. VAUCHERIACEJE. 



The thallus is an elongated filament consisting of a single large 

 ccenocyte, and is sometimes branched. This unseptate filament 

 increases in length by apical growth and is usually attached to a 

 substratum by much branched haptera. In most members of the 

 family the cell-wall is thin and relatively weak, easily collapsing 

 even with careful manipulation. The protoplasm forms a thick 

 lining layer on the interior of the wall of the filament and contains 

 a large number of minute nuclei. The chloroplasts are very small 

 and exceedingly numerous ; they are oval, elliptical or subcircular 

 in outline and are without pyrenoids. A considerable amount of 

 oil is often present in the filaments, the oil-drops being always in 

 connection with the chloroplasts. Fleissig 1 states that this oily 

 material is a reserve substance, physiologically analogous to starch. 



On the injury of the thallus septa usually appear cutting off 

 the injured parts, the uninjured portions developing into new 

 plants, (vide fig. 42 A and B.) These are the only instances of 

 the occurrence of septa in the thallus except in connection with 

 the reproductive organs. 



Asexual reproduction takes place by the formation of zoogonidia. 

 The extremity of a filament assumes a club-shaped form and 

 becomes densely filled with protoplasm, after which a transverse 



1 Fleissig, 'Ueber die phys. Bedeutung d. oelartigen Einschliisse in d. Vaucheria,' 

 Basel, 1900. 



