the climatic zonation. Also that of the different great groups of the Flower- ing plants the Monocotyledons are predominantly tropical, the Sympetalae least so, and this lagging behind by the Monocotyledons in escaping from the tropics may perhaps be explained by the vastly greater proportion of aquatic orders in this group, though this is probably not the whole explanation.
The paper begins with a reference to papers on the distribution of the Compositae, by Bentham and of Gentianaceae by Huxley, in both of which an original even distribution of the family was postulated, and the work of Dr. Willis on the Podostemaceae, which in spite of absolutely uniform condi- tions show the greatest amount of floral and other differentiation is quoted as lending support to the idea that in an age of great uniformity of conditions it might be possible to have the greatest instability of essential characters, which later on became fixed with the gradual progressive differentiation of
conditions.
P. F. F.
Ecology.
Sedgwick, L. J., Analyses of some morphological characters of Bombay woody species from an Oecological stand-point. Indian Forester 1919 pp. 193—9.
This paper arose the author says 'from a desire to test the 'drip-tip' theory of Stahl ' but he included investigation on armature and methods of seed-dispersal. The leaf-tip he classifies under seven heads from ' very long acuminate' to very obtuse with an eighth class of plants leafless in the mature state, for xerophytes. Acute or acuminate tips are a feature of the evergreen forests of his region (with 83 per cent.), but among xerophytes there are 35 percent, not much fewer than with obtuse apices (41 per cent.); and the author believes the acuminate leaf-apex is only the result of general good development owing to favourable circumstances at the end of the chief vascular bundle. Thorns and spines too he finds chiefly developed among xerophytes but also in some evergreen trees, and since goats and camels eat thorny Acacias without seeming to mind the thorns, he denies in this case too any teleological explanation, and puts down the hardening of the thorns simply to the tendencies of general development. To this most people will probably agree, for that the development of spines and prickles is furthered, and even initiated, by dryness has been proved by Lothelier with TJlex, and by other workers.
P. F. F.
Histology
Balls, W. L., Growth-rings in the Cell Wall of Cotton Hairs Proc. Bag. See B. 90 No. B 634, p. 542 with 4 text-fig and 5 mino- photographs.
By suitable treatment of cotton hairs to make the wall swell, the author demonstrates Ithe existence of concentric layers, corresponding to the daily growth in thickness of the cell-wall interrupted as it is each afternoon by the sun-heat. Previous work had shown that the growth in thickness of the wall, and the formation of simple pits began on the 21st to 25th day of the
