62 THE JOURNAL OF INDIAN BOTANY. 



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 



