Page:The Journal of Indian Botany.djvu/37

 few plants can grow. Rhododendrons grew however to 13,000 ft. Among the plants of this region were species of Achronychia, Pilea, Elatostema, Rabus lmpatiens, Symplocos, Habenaria, Ilex, all of which genera occur on our South Indian mountains at much lower levels. The flora falls into three groups, an Australian, an Antarctic and a Palaearctic.

Over 500 new species are described, and it is considered that New Guinea with its adjacent islands should be considered a " distinct region of its own with a large endemic flora revised with derivatives from Malaya, Australia, and Pylynesia, and, possibly through the Philippines, from the temperate regions of the North." P. F. F.

Ecology.

McLean, R. C. Studies in the Ecology of Tropical Rain Forest. Journal of Ecology VII. {1919) pp. 5 — 59.

This very interesting paper is the first of a series on the ecology of the tropical Rain forest (as developed near Rio de Janeiro). It is a record of careful work and full of suggestive ideas. Records were taken by self-recording instruments of the humidity inside and outside the forest, the former at both a low-level of 1 metre, and a high level of 4 metres, above the ground. The low-level instrument as might be expected showed much small range of variation than the high, and at the latter level the humidity was greater on the whole but much more variable than that in the city of Rio. The incessant variations in humidity the author puts down to the effect of flecks of sunlight piercing the canopy of leaves, and he considers that these variations have a marked effect on the ecology of the under-growth. Elaborate calculations and measurements of the diffusion capacity of the stometa, the volume of inter-cellular spaces in the mesophyll, and the area of cross section of the xylem portion of the vascular bundles of the petiole, in shade and in sun plants, are given, and show that in these plants of the under-growth capacities for absorption and conduction of soil-water are developed only on a low scale.

They possess no adaptation towards increasing the amount of trans- piration, tut are commonly protected by a thick cuticle. This may be explained as due to the frequent short periods of insolation by sun-flecks which by lowering the humidity, in conjunction with the fact that the chlorophyll in shade leaves is more exposed to their influence than in habitual heliophytes, may cause the loss of water to be greater than the roots can supply. This failure to obtain more water from the soil " seems to point to edaphic factors antagonistic to absorption." The author goes on to say that a shortage of mineral matter might be expected, but examination shows that there is a higher content of ash in relation to the weight of assimilates than in helophytes ; so that the absorption of mineral salts appears to be independent of foliar evaporation. In other words the roots exercise a selective action. This of course is no new idea. Among other interesting points touched on is the effect of a nyctitropic position on transpiration, where the author finds to be negligible, and to have no significance in regard to water-loss. He thinks that the vertical position may prevent the closing of the stomata by too rapid transpiration during the early sunshine hours when assimilation should be active. Another is the large amount of moisture transpired