1905] PEIRCE & RANDOLPH—IRRITABILITY IN ALGAE 3.43 
the mother cells, conditions which may have induced a polarity in 
the spore, but a polarity which is not so fixed that subsequent influ- 
ences cannot alter it. 
Influence of contact on germinating spores.—From the work in 
fresh-water algae reported in the foregoing pages, one is led to suspect 
that the character of the surface with which the rhizoids of germinating 
spores of marine algae come into contact will largely determine the 
shape and completeness of attachment of the holdfasts. The strength 
of the holdfasts as the plants mature is determined not merely by 
the surface but by other factors. Among these may be mentioned 
the movement of the water in currents and waves, the size and shape 
of the plants, and all other factors which affect the strain which the 
holdfast must withstand.? But the first attachment of sessile algae, 
whether marine or fresh water, is greatly influenced by the roughness 
of surface. I was first led to suspect this by the extraordinary freedom 
of Spirogyra and Iridea—the smoothest, most slippery fresh and salt 
water algae, respectively, which I know—from diatoms and other 
sessile plants growing upon them. Cladophora and Microcladia, 
comparatively rough forms, show the direct opposite. 
To test this hypothesis with marine algae, I put in the bottoms 
of the glass dishes used for cultures cover glasses 18X18™™ square, 
which had been carefully ground on one side ona stone. One half 
of the cover glasses were put smooth side up, the other half rough side 
up. At first I used the cover glasses only rough side up, letting the 
smooth glass of the dishes furnish the other surface. This plan 
Seemed open to objection, as the glass of the dishes might not have 
the same composition as the material of the cover glasses, and the 
light would not be the same on a ground surface as on a smooth. This 
latter objection is not wholly eliminated even by using thin cover 
glasses, but it is as nearly eliminated as at present possible.* . The 
a co. (z, p- 395) has felt obliged to retract his published rena a 
aims ck ¢ - laboratory by the late R. HEGLER (6), sae i soa by ana- 
tomical changes ; sf e rs ee aa of increased mene as 3 a ag us steal 
thow that ee but I may venture to express the Dele® © ae 
nd HEGLER and not PFEFFER and Batt (1) were Ng 
in man can be and was eliminated in certain cultures nd oe ee 
introduces sess ae were similar to those in the light, but darkness 
s if prolonged. ; 
