9 o PLANT PHYSIOLOGY 



300, 1. 42, after thermotonus read (comp. A. MEYER, 1906) ; 



1. 47, for killed rapidly . . . others may read killed rapidly, when kept for 

 long in a state of cold rigour, others may 



301, 11. 12-22, for [MEZ (1905) ... of the question, read According to 

 MEZ (1905), however, the freezing of frost-resisting plants is not due to the 

 withdrawal of water, for death often takes place in these forms at a temperature 

 which lies far below that at which all water must be crystallized out. In 

 opposition to MULLER-THURGAU, who held that the formation of ice was con- 

 tinuously proportional to the decrease in temperature, MEZ attempted to show 

 that at 6 C. all water is crystallized ; further research must determine whether 

 that is the case or not. Further, according to MEZ, the formation of ice is a 

 distinct advantage to the plant, inasmuch as ice conducts internal heat more 

 slowly than the fluid cell-sap. The fatty oil which appears, e. g., in many trees 

 in winter, must tend to prevent excessive cooling of cell-sap, inducing an oppor- 

 tune formation of ice, and therefore lowering the freezing-point in the plant. 



Last line P. 302, 1. 42, for Indirectly it is ... rest of the protoplasm. 

 read In the case of those organs on which light falls, especially the leaves, light 

 would appear, at least at first sight, quite essential. As WIESNER has shown 

 in a number of researches (1893-1905 ; summarized in 1907) the development 

 of the shoot under natural conditions takes place only when the light is of a 

 certain definite intensity, which varies very greatly according to the nature of 

 the plant. WIESNER'S great service lies in his having accurately measured 

 this intensity. For this purpose he employed the Bunsen-Roscoe method, 

 which, it is true, is adapted to the study of the more highly refrangible rays, 

 those, that is to say, which act on silver salts. WIESNER has determined both 

 the absolute and the relative light intensity under which a plant will thrive in 

 different surroundings. The light intensity, as measured by the Bunsen- 

 Roscoe method, he terms the absolute ' photic ration ' ; the relative photic 

 ration (L), on the other hand, is what range of the total light the plant can 

 flourish in. 



If the plant can live, for example, on the one hand in full illumination, and 

 also in ^ of that, WIESNER says that its relative photic ration lies between 

 i and j 3 ^. 



Then read P. 307, 11. 42-51. 



Shade plants such as the beech can put up with ^ of the light intensity 

 that light -loving plants prefer. The beech can thus grow normally in diffuse 

 light without any exposure to direct sun's rays (WIESNER, 1904). 



Then read P. 307, 1. 52 P. 308, 1. 9 (For one . . . impossible), and follow 

 on Branches of the plants above mentioned, however, grow under experi- 

 mental conditions under light of much less intensity than what they are sub- 

 jected to in nature. WIESNER (1904) has shown that in the case of the maple, 

 no buds expand under natural conditions if the relative photic ration be less 

 than -J^. Experimentally, however, buds do open with a relative photic ration 

 of ^-i^, and indeed attain their normal form ; they bud out as well in complete 

 darkness, although they certainly assume at the same time an abnormal appear- 

 ance, which has already exhibited itself when the relative photic ration = 1^0- 

 This remarkable difference between the developmental behaviour of buds under 

 experimental and under natural conditions is due, on the one hand, to the 

 varying relationships existing between individual buds, and on the other to a 

 certain stimulatory effect of light. Buds which are well illuminated sprout 

 rapidly and prevent those less brilliantly illuminated from doing so. If, how- 

 ever, these relations be interfered with, as by darkening all the buds, it may 

 then be seen that light is in no respect a condition of growth of the shoot. 



Many other observations which appeared to indicate the dependence of 



