346 BOTANICAL GAZETTE [NOVEMBER 
holdfasts may develop as on ground glass. When I saw the plant 
shown in jig. 26a, I thought my hypothesis was disproved, for here we 
have as elaborate a holdfast as on ground glass. On examining the 
plant with a stronger magnification, I found, as fig. 26b shows, that 
diatoms or diatom-shells were very numerous on the glass at this 
point, making it rough, or rather covering it with obstructions to the 
growth of the base of the plantlet. This plant and the many others 
like it confirm my belief that roughness of surface stimulates the sessile 
algae firmly to attach themselves. 
It must be noted, however, that ground cover glasses kept in 
cultures for a week or so become slimy; their roughness is reduced or 
concealed by a thin, very smooth coat, which must be dissolved off 
before one can use the cover glasses again with the maximum effect. 
Even when all “dirt” and diatoms are washed off, the cover glasses 
are not clean as they are when new; they must have the slimy coat 
removed too. This is easily done by boiling in fresh water for a few 
moments. On the other hand, diatoms, animal excrement, and fine 
dirt generally, often so roughen the unground surface of glass as ' 
induce holdfast formation of marked character. 
When for any reason, such as the extreme smoothness of the glass 
or the absence of any contact whatever, the elongation of the thizods 
is not stopped, they may attain surprising lengths and often ina 
short time. Fig. 25 shows such an extraordinarily long rhizoid 
Dictyopteris. Fig. 27 shows us two plantlets of Dictyota dicholom? 
growing on the same smooth side of a cover glass. In the one eee 
the rhizoid soon came into contact with small particles of dirt sticking 
to the glass, and thereupon ceasing to grow in length, formed a typi 
holdfast. In the other case, no dirt caught the rhizoid, which con- 
tinued to grow over the smooth slime-covered glass. - 
I may here say something about the amount and the rate of grow 
of these germinating spores. On November 5th, = . oe 
twelve, I made a camera drawing of a spore of Dictyola ae nest 
Four hours later I similarly drew the same spore. And g This 
ng. - 
cent. 
morning at a quarter to eleven o’clock I made another draw! 
