352 BOTANICAL GAZETTE [MAY 
mperes per cm?-sec. He finds the positive curvature constant and shows 
clearly that it is due to injury of the cells on the positive side. He does not find 
the negative curvature constant in any case, but observes that the positive curva- 
ture (which he calls normal) may be produced, even when the negative appears, 
by varying the strength and time of action of the current. This GASSNER 
confirmed, but he paid more attention to the negative curvature as the initial 
effect of very weak currents, and lays stress on it in identifying galvanotropism 
with traumatropism as an irritable phenomenon. 
PLowMAN ascribes the injury causing positive curvatures to positive electrons 
bombarding the side of root turned toward the anode (wherefore he prefers elec- 
trotropism). He specifically denies the influence of products of electrolysis. 
Negative electrons he finds innocuous and perhaps even stimulative. Thus 
facts are mainly corroborated by GASSNER, but the two interpretations are quite 
different. GASSNER also seems to have entirely overlooked PLowMAN’s papers.— 
R. B 
Morphogenesis in Ceratophyllum.—A recent publication by the Carnegie 
Institution,"® under the authorship of Dr. Peart and assistants, proves to be a 
contribution of unusual merit because of the masterly way in which the bio- 
metrical method has been applied to one of the most important but neglected prob- 
lems of biology. Two laws of growth in Ceratophyllum have been formulated 
on the basis of convincing evidence. The first law is: ‘“The mean number of 
leaves per whorl increases with each successive whorl, and in such a way that not 
only does the absolute increment in each leaf-number diminish, but also the rate 
of increase diminishes as the ordinal number of the whorl, measured from a fixed 
point, increases.” The second law is: “As whorls are successively produced by a 
growing bud, they are formed with ever-increasing constancy to their type, the 
ultimate limit towards which the process is tending being absolute constancy.” 
The significance of these laws and the field for physiological study suggested by 
them is far too great to be elaborated here and reference to the original is urged. 
The paper shows a clear scientific discernment and is a model of composition. 
It may safely be said that the Carnegie Institution has not wasted any money on 
this minor grant. The value of such a contribution as compared with its insig- 
nificant cost goes far toward compensating for the cost of other small grants which 
have proved less fruitful—Raymonp H. Ponp. 
Relation of saprophytic fungi to the substratum.—T wo papers have appeared 
dealing with the relation of some saprophytic fungi to their substratum. The 
first of these, by Kratz,’ deals with pyrenomycetes growing on dead stems of 
herbaceous plants and on leaves. It consists mostly of brief categorical descrip- 
8 PEARL, RAYMOND, with the assistance of OLIVE M. PEPPER and FLORENCE J. 
HAGLE, Variations and differentiation in Ceratophyllum. Pub. Carnegie Institution 
of Washington no. —. pp. 136. 1907. 
_ _19 Krantz, Cart von, Ueber die Beziehungen der Mycelien einiger saprophy- 
tischer Pyrenomyceten zu ihrem Substrat. Hedwigia 46:1-24. figs. 8. 190 
