530 THE AMERICAN NATURALIST. [VOL XXXII. 
fibro-vascular zones arise from the pericycle), the dicecious flowers, 
pentamerous calyx, absence of corolla, indefinite stamens, solitary 
ovules, apical position and caducous character of the stigmas, 
exalbuminous seeds and accumbent cotyledons. Several of these 
features, however, do not appear to have in the present case much 
diagnostic value. For instance, nothing can be argued from the 
absence of petals, since these members are either lacking or ex- 
tremely rudimentary in the other Buxacee. As to the indefinite 
stamens, these occur also in Styloceras, which is furthermore sub- 
diceecious. Nevertheless, enough good distinctions remain to show 
a rather wide gap between Simmondsia and the other genera of the 
group to which it has long been referred. 
The tendency to make new families of divergent or anomalous 
genera is of late very pronounced. ‘Thus, in the interval between 
the issue of Engler & Prantl’s Watiirlichen Planzenfamilien and the 
supplement of the same work, a rather large number of these small 
and often monotypic “families”? have been suggested. The crea- 
tion of such families, if followed by no rearrangement, is of doubt- 
ful practicality, and likely to complicate rather than to clarify 
classification. It is otherwise, of course, in cases like the present, 
where a composite group must be divided in order that its parts 
may be more naturally: distributed in relation to allied families. 
B. L. R. 
Contact Irritability in Hook Climbers.!— In this article Dr. 
Ewart gives an exhaustive account of the phenomena of contact 
irritability presented by certain tropical hook climbers which he 
investigated at Buitenzorg. Treub was the first to call attention to 
the fact that the hooks of certain climbing plants thickened and 
became stronger when fixed to some support. His work having 
been mainly morphological, Dr. Ewart has taken up the physiological 
aspect of the question. 
This involved the consideration of the effect of variation in the 
intensity of the stimulus applied; of the transmission and ultimate 
effect of such stimuli on the growth of the parts concerned. The 
stimulus afforded the plant under its natural condition, that brought 
about by the usual artificial mechanical devices, and, in addition, the 
stimulation caused by injury, all received attention. The reaction 
is observable in the inequilateral increase of growth of the hooks, 
1 Ewart, A. J. Contact Irritability. Ann. du Jard., Bot., de Buitenzorg, vol. xv, 
i, pp. 187-242. 
