418 The Botanical Gazette. [September, 
and the water suspension cultures. In the’ one, rhizoid-like 
outgrowths were obtained in all cultures (thirty-one) of Spir- 
ogyra fluviatilis Hilse, S. inflata(Vauch.) Rab., S. orthospira 
Naeg., and in four undetermined species. In the other, in no 
case did the formation of rhizoids result. In some cases wa- 
ter suspension cultures which showed no result, when trans- 
ferred to contact cultures developed rhizoids in from two to 
four days. : 
That other conditions influence this development is shown 
by the growth in different media, the required density differ- 
ing with the different media, as well as with the Species; ¢. fo 
in agar-agar, the lowest limit favorable to the formation 0 
rhizoids, was a .05 per cent. solution, while for a gum solu- 
tion it lay between .5 and 25 per cent. 
The development of rhizoids by contact culture was also 
attempted under the influence of darkness, but the conditions 
were unfavorable for the development of the filaments cade 
selves although in some cases rudimentary rhizoids occurre 
during the first few days. h 
One of the most interesting results derived from the researc 
was in connection with S. vardans (Hass.); in this species sa 
thizoids were developed, but, contrary to the statements 0 
Vaucher, Pringsheim and DeBary, the author concludes gat} 
observing the germination of the zygote in three different cul- 
tures that the so-called ‘‘rhizoid cell” of the germinating tube 
does divide to form the cellular increase of the filament. ‘ 
Cultures of Zygnema showed no rhizoid growth. In io 
cultures of Mougeotia the rhizoids were also conditioned é 
external mechanical influences since none were formed excep 
in contact cultures. 
Similar cultures were made of Vaucheria and of those for et 
in which the formation of rhizoids is more or less normal; 
2. é., Cladophora, Draparnaldia, CEdogonium and Ulothrix. 
While no rhizoids were obtained on mature threads of Vaw- 
cheria clavata (Vauch.) DC., their presence was observed sei 
germinating filaments. On V. sessilis (Vauch.) DC. non 
were produced under any circumstances. Both old andy oung 
threads of Cladophora, Draparnaldia, and Ulothrix forme 
rhizoids under all conditions. n 
of CEdogonium rhizoids were formed in all cases but the 
property seems to have become lost in older threads. be 
n summing up, the author advances the theory that t 
