G52 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the samo weight of living tissues differ very considerably with the 

 stage of development, and usually pass through successive maxima 

 and minima. The most important maxima correspond with the 

 commencement of germination and flowering respectively. These 

 are also the stages at which respiration is most intense, but if the 

 quantities of heat corresponding with the amount of carbonic anhydride 

 evolved in a given time are compared with the heat actually developed 

 during the same time, there is never any sensible agreement between 

 the two quantities. The quantity of heat developed is not equal to 

 that which would be produced by the combustion of the carbon lost 

 by the organism. 



At the commencement of germination, the heat actually developed 

 is much greater than that calculated from the amount of carbonic 

 anhydride evolved, and even greater than that which would be 

 developed by the combination of carbon with the whole of the oxygen 

 absorbed during germination ; but after germination, and during the 

 formation and maturing of the fruit, the reverse is the case. 



These facts agree with the hypothesis that the reserve substances, 

 which are not directly assimilable, are usually formed in the 

 organism with absorption of heat ; whilst the transformation of these 

 substances into assimilable materials is accompanied, as a rule, by a 

 development of heat. During the consumption of the reserve sub- 

 stances, as at the commencement of germination, the heat developed 

 by the transformation of these substances is added to that developed 

 by the formation of carbonic anhydride ; but whilst reserve substances 

 are being formed, as during the maturing of the fruit, the heat 

 actually developed is the difference between that absorbed in the 

 formation of the reserve material and that developed by the formation 

 of carbonic anhydride. 



Movements of the Tendrils of Cucurbita.* — From observations 

 of the movements of the tendrils of Cucurbita maxima and Pepo, 

 Prof. D. P. Penhallow has come to the following general conclusions : 

 — Growth is promoted by an increase of temperature and humidity, 

 but may be retarded by an increase of temperature when other 

 conditions are not favourable. The conditions favourable to growth, 

 arising from temperature and humidity, may cause greater growth 

 during the day, in opposition to the retarding influence of light. 

 Growth is retarded by excessive transpiration. The conditions to 

 which the plant is subject being variable, there is a corresponding 

 periodicity in the vital phenomena. Movements of tendrils and 

 terminal buds, being phenomena of growth, are modified by whatever 

 variations of condition affect growth. 



The term vibrogen is given by Prof. Penhallow to certain areas of 

 tissue in the tendrils immediately beneath the epidermis, composed of 

 rather large and rounded parenchymatous cells with somewhat thin 

 walls, and containing protoplasm and a large amount of chlorophyll, 

 which appear to play an important part in the movements. 



With reference to circumnutation of the tendrils, movements of 



* Amer. Jouru. Sci., xxxi. (1886) pp. 46-57, 100-14, 178-89 (1 pi.). 



