392 BOTANICAL GAZETTE ; [OCTOBER 
penetration by the masses of fungal filaments. Vegetation thus destroyed is 
replaced, after the death of the fungous, first by weeds, then by short-lived 
grasses, and eventually by the original short-grass cover.—H. C. Cowles. 
Foreign pollen on Cycas.—It is well known that in some cycads the ovules 
reach the maximum size for the species whether pollination has occurred or not; 
while in others the ovules, if not pollinated, soon disorganize. Cycas Rumphii 
belongs to the latter category.* Female plants of this species are very abundant 
in Ceylon, but no male plants have been observed for several years. In local- 
ities where male cones of Encephalartos and Macrozamia are abundant, the 
pollen of these species germinates in the pollen chamber of Cycas Rumphii 
and causes the ovule to develop to the full size. Since the pollen of cycads 
germinates readily in artificial solutions, it is not strange that pollen of one 
species should germinate in the pollen chamber of another. In this case, 
however, no fertilization takes place, and mature seeds, which should show the 
embryo in an advanced stage of development, showed no trace of an embryo. 
A few years ago the reviewer pollinated Stangeria with Zamia and obtained 
three large seeds, which were planted but failed to germinate. It is possible 
that the pollen stimulated growth but failed to fertilize the egg, so that, as in 
Cycas Rumphii, no embryo was produced.—CHARLES J. CHAMBERLAIN. 
Water culture.—In a critical discussion of the water culture method of 
studying growth phenomena, STILES" calls attention to the limitations of the 
method. He points out the great complexity of the factors involved, and 
applies BLACKMAN’S idea of limiting factors. The difficulty of analyzing the 
results of such experiments, due to the interaction of so large a complex of 
factors, few of which, even those whose action is under investigation, can be 
controlled, is made clear. Some factors, as for instance the influence of the 
respiratory activity of the roots on the culture solutions, have been neglected 
in all water culture work. The variability of individual plants is so great that 
a large amount of labor is required to secure results even with a low degree of 
accuracy. Nevertheless, for certain kinds of problems it may be the only 
method available——Cuartes A. SHULL 
Grasses of Illinois.—Miss MosHEr” has published a manual of the grasses 
of Illinois, recognizing 204 species in 63 genera, over one-fifth of the species 
being recorded for the first time as occurring in Illinois. The analytical keys, 
escriptions, and numerous text age make the bulletin very useful in the 
recognition of the grass flora.—J. M 
* Le Goc, M. J., Effect of foreign pollination on Cycas Rumphii. Ann. Roy. 
Bot. Gard. Peradeniya 6:187-194. pl. 13. 1917. 
‘9 STrLES, WALTER, On the interpretation of the results of water culture experi- 
ments. Ann. Botany 30:427-426. 1916. 
, Epna, The grasses of Illinois. Univ. Ill. Agric. Exper. Sta. Bull. 
205. pp. Paty Sigs. 287. 1918. 
