CUERENT LITERATURE. 27 



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 assimi- 

 lates 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 assi- 

 milation should be active. Another is the large amount of moisture transpired 



