AGRICULTURAL BOTANY. 821 



seem to be best adapted to germination in strong illumination, while P. excelsa 

 prefers a feeble illumination or darkness. The seed of C. arborescens seems to 

 be adapted to germinate equnlly well in the light or in the dark. 



The effect of freezing seed on their germination and the relation be- 

 tween frost influence and light influence, W. Kinzel {Prakt. BI. Pflanzenban 

 u. Schutz, n. SC7'., 9 (1911), No. 8, pp. 105-llJt). — This is a detailed account of 

 recent and extensive investigations by the author on seeds of 375 species rep- 

 resenting many families. These were made for the purpose of ascertaining the 

 several and joint effects of temperature (especially below the freezing point) 

 and light on the time and percentage of germination of such seeds, having in 

 view their bearing upon the control of agricultural weeds, numerous species of 

 which were represented in the test. 



With many kinds the minimum or absence of light seemed as essential to 

 germination as its abundance to others. With some, also, a period of exposure 

 to cold appeared to be as essential to ultimate germination as a subsequent 

 period of warmth, in concurrence with other necessary conditions. The various 

 combinations of these factors gave results which were numerous and practically 

 suggestive. 



The investigation of a climatic gradient, F. Shreve (Abs. in Science, n. 

 ser.. 33 (1912). No. 891, pp. 157, 158). — The author describes the distribution of 

 plants on the slope of the Santa Catalina Mountains, stations being located at 

 intervals of 1,000 ft. and the temperature, rainfall, soil moisture, humidity, 

 evaporation, and soil temperature determined. 



It is claimed that the factors of soil moisture supply and atmospheric humid- 

 ity, modified by slope exposure, determine the lower limits of forest and the 

 trees of the chaparral zone. The factors of winter cold, modified by topog- 

 raphy through the operation of cold-air drainage, determine the upper limits 

 of the characteristic desert species. 



The nature of the absorption and tolerance of plants in bogs, A. Dach- 

 NowsKi (Abs. in Science, n. ser., 35 (1912), No. 891, p. 156). — The author claims 

 that a study of the quantitative nature of habitat factors, which are rightly 

 desired as a basis for a theory of physiologically arid habitats, does not explain 

 the nature of the absorption of plants in bogs and the nature of their tolerance 

 to toxic substances in peat soils. The phenomena of absorption and of resist- 

 ance to desiccation deal with considerations of the permeability of the absorb- 

 ing protoplasmic membrane, its power of endurance, and its ability to trans- 

 form the injurious bodies into insoluble, impermeable compounds. 



Observations on evaporation and transpiration in prairie and forest, R. 

 Shimek (Abs. in Science, n. scr., 35 (1912), No. 891, p. 157). — An effort has 

 been made to determine the differences between forest and prairie plants which 

 would account for their distribution, observations being made on the transpira- 

 tion on certain forest and prairie plants in their native habitats and their 

 transposed ones. Two stations were selected on a ridge, one side of which 

 is prairie and the other forest, one station being located in each. Two plants, 

 one from the forest and one from the prairie, were placed at each station, and 

 the loss of water was determined at 2 hour intervals. In addition to this, 

 observations were made at each of the stations on evaporation, and the meteor- 

 ological conditions affecting it. 



The general results showed that transpiration and evaporation are not 

 coincident. 



Shade as a factor influencing evaporation, G. P. Burns (Abs. in Science, n. 

 ser., 35 (1912), No. 891, p. 157). — A description is given of some experiments 

 to determine the evaporation in forest nurseries, in which plants were sub- 



