Con piepaole an auntie ie tesa 
eae: of me ee Tt — however, is having distinct 
1897 ] SOME NEW SPECIES OF MINNESOTA ALGAE 103 
A still more curious alga is one which inhabits the white 
sandstone cliffs at a point where Minnehaha creek flows into 
the Mississippi river. The rock presents no trace of plant life 
on its outer face, which has the usual appearance and light gray 
color of weathered white sandstone. But small pieces broken 
off and held up to the light show fine colorless threads hanging 
from the inner side of the fragments. These are filaments of a 
Schizothrix. The plant is found at least one-half inch from the 
outer surface. The amount of light received by it is necessarily 
extremely small, for the reflecting surfaces offered by the crys- 
tals are very numerous in such a thickness of stratum. 
. There is some difficulty in extracting the algal threads from 
the sand grains. The only satisfactory method is to moisten a 
bit of the material and place it under the low power of the 
microscope. The grains can then be removed with a needle, 
allowing the filaments to remain. It is necessary to use a +, 
oil immersion lens in order to observe the dissepiments. 
Schizothrix rupicola Tilden, Am. Alg. Cent. II. no. 175. 1896 
(pl. LX., fig. 9)—No definite stratum. Filaments 9.6-16 in 
diameter; sheath cylindrical, rough, for the most part hyaline, 
sometimes brownish and much lamellated; trichomes pale xru- 
ginous, one to many in a sheath, not constricted at joints, 3.5— 
4.8 in diameter; articulations I-1.5 times as long as wide, 5-8 
long; dissepiments for the most part invisible; apical cell trun- 
Cate conical or rarely somewhat attenuate. 
Bare and dry sandstone cliffs, not on surface of rock, but extending 
within the interior to a distance of at least 1o-15™™. Collected by Prokeaper 
C. W. Hall, Sept. 28, 1896. a 
icola agrees with S. Friesii in the diamet i length of artic- 
Pe Sanit in the shape of the apical cell; ‘but the trichomes do not display a 
the constriction at the dissepiments which is so evident in the Jatter species, 
nor are the dissepiments themselves so conspicuous, it being nearly impos- 
lens. Furthermore, 
— to observe them even under the pe oil immersion 
itat. > S. rubella is likewise similar i in the ued 
