574 SUMMARY OF CURRENT RESEARCHES RELATING TO 



increase from July to September ; from this time, when the weight of 

 dry matter remains constant, the former regularly diminish and are 

 replaced almost exactly by cellulose. 



Irritability. 



Effect of Sunshine on Plants.* — N. Passerini publishes some ob- 

 servations upon the results of growing thirteen different species of 

 plants in direct sunshine and in diffused lifrht respectively. By analysis 

 he determined the relative percentages of water, organic matter, and 

 mineral ash of the two sets of plants. The highest gain was found in 

 Cncurbita Pejio, where the plant grown in sunshine was twenty-seven 

 times as heavy as the shaded plant ; and the next were Hordeum vulgare 

 and Zea Mays where the gain was about nine times. As to gain in 

 organic substance, the greatest gains were shown by Brassiea Bapa, 

 Hordeum vulgare, and Anagallis arvensis. The conclusions drawn by 

 the author are that in every case the plant exposed to direct sunlight 

 is heavier tban the shaded plant ; that the failure of direct radiation 

 limits the growth of the plant, and retards the vegetative phases, 

 especially the inflorescence and the complete development of the fruit ; 

 that the sun-grown plants are much greener than the shaded ; that the 

 shaded plants have a larger proportion of water and less of solid sub- 

 stance ; that the higher percentage of solid substance in the sun-grown 

 plants is chiefly due to organic matter ; and that the difference in the 

 proportion of mineral matter is less notable. 



Electrical Phenomena in Plants.f — A. Tompa has studied electro 

 motive effects in dead and living seeds. He finds that there is no 

 essential difference of intensity in manifestation of electric polarisation 

 in living and in dead seeds respectively. The polarisation currents in 

 both living and dead seeds may reach considerable intensity, but are of 

 small tension. The amount of intensity and the direction of the current 

 vary according to variations in the internal resistance of the seeds. A 

 criterion of the life of the seed is supplied by the " lesion "-current ; 

 in the case of living seeds, as a result of superficial injury on one side, 

 an electromotive force with a potential exceeding - 005 volt is expe- 

 rienced, while dead seeds show no potential, or at any rate one of less 

 than • 005 volt. Hence a lesion-current whose potential exceeds ■ 005 

 volt may be considered a criterion of life in a seed. 



Electric Response in Plants under Mechanical Stimulus.* — J- C. 

 Bose describes apparatus and experiments on numerous plants, which 

 prove that plants and their different organs give precisely the same 

 electric responses to stimuli as does animal tissue, indicating that vital 

 phenomena are identical in the animal and plant kingdoms. That the 

 responses are physiological, and not merely mechanical, in character is 

 shown by the fact that whatever tends to exalt or depress the physio- 

 logical activity, tends also to increase or diminish the electric response. 

 The effect of anaesthetics and poisons, organic variations, fatigue, modifi- 

 cation by liigh and low temperatures, corresponds strictly to similar 



* Bull. Soc. Bot. Ital., 1902, pp. 13-24. 



t Bcih Bot. Centralbl., xii. (1902) pp. 99-136 (3 figs.). 



t Joiu-n. Linn. Soc. (Bot.), xxxv. (1902) pp. 275-30-i (25 figs.). 



