644 EXPERIMENT STATION RECORD. 



at many different altitudes, lie lias measured the amount of fight falling upon a 

 plant and the total illumination during the day, and the proportion between these 

 two factors he proposes calling "pliotolepsis." This factor when presented as a frac- 

 tion can never be greater than 1, and it is found to vary with different plants at dif- 

 ferent altitudes and latitudes. 



The minimum of photolepsis at Vienna was determined for Pinus laricio as ,',, for 

 Acer platanoides 55, and for Buxus sempervirens ,,',,,. The minimum is always the 

 lowest for deciduous trees and it varies materially with the period of leaf growth, 

 temperature, latitude, etc. At the beginning of leafing the maximum photolepsis for 

 Acer platanoides is 1. At Vienna in early spring it was found to he ,',,, and it fell to 

 -,'-, later in the season when in full leaf. At Trondhjem, Norway, it had a stationary 

 value of iV* while at Tromsoe, Norway, it was \. This proportion is approximately 

 constant. 



The author concludes that the adaptation of a given plant to intensity of light can 

 not be expressed by a definite optimum, but it is modified by climate, temperature, 

 surrounding medium, etc. Further, the adaptation is influenced by the diffused 

 light in which most plants grow. He holds that plants are continually subjected to 

 changes in light intensity and believes that few plants receive a definite optimum of 

 light. 



Perception of the force of gravity by plants, F. Darwin {Nature [Loudon], 70 

 (1904), No. 1819, pp. 466-473, figs. 3). — In an address before the Section of Botany 

 of the British Association for the Advancement of Science, the author summarized 

 the various hypotheses relative to the perception of the force of gravity by plants. 



Considerable attention was paid to the statolithic theory, which is based on the 

 difference in specific gravity of the nucleus, chloroplasts, crystals, starch bodies, etc., 

 occurring in the cell sap. These will exert pressure on the physically lower or 

 higher cell walls according as they are heavier or lighter than the cell sap. As long 

 as the stem is vertical and the apex upwards the heavier bodies rest on the basal 

 wall and the plant is not stimulated to curvature. If the plant should be placed 

 horizontally so that the heavy bodies rest on the lateral cell walls, the plant is 

 stimulated to curve. 



This hypothesis was discussed at length and experimental evidence cited to sub- 

 stantiate it. The author attributes the fundamental principles of this hypothesis to 

 Haberlandt and Nemec, and in conclusion states that "this may fairly hold the 

 field until a better theory of graviperception and a better theory of the falling of 

 starch grains are established." 



The distribution of the more important materials in kohl-rabi and carrots, 

 Zielstorff and Beger (Fuhling's Landw. Ztg., 53 (1904), No. 13, pp. 491-495). — 

 Studies are reported on the distribution of the dry matter and nitrogen-free extract 

 in kohl-rabi and carrots. The plants were divided into tops, crowns, and roots, 

 which were subdivided into cortex and inner parts, and the percentage of dry 

 matter and nitrogen-free extract determined. Considerable variation was noted in 

 the content of the different parts of the plants, and this is believed to be an impor- 

 tant consideration in experiments in plant breeding. 



The influence of assimilable nitrogen on the action of root tubercle bacteria, 

 F. Nobbe and L. Richter (Landw. Vert. Stat, 59 (1903), No. 3-4, pp. 167-174) — 

 Investigations have been carried on upon the influence in the soil of assimilable 

 nitrogen on the action of root tubercle bacteria. 



The authors give the results of 3 series of pot experiments which were conducted 

 with hairy vetches, and aside from the nitrogen present in the soil or added to the 

 pots the treatment in all cases was the same. Where a large amount of assimilable 

 nitrogen was added, there was a relatively lessened nitrogen assimilation for the 

 inoculated pots and an increased assimilation for the uninoculated ones, although 



