242 BOTANICAL GAZETTE [September 



ions. Since the plant body is electro-positive to the soil, the negative elec- 

 trons are being discharged to the plant in its normal physiological activity 

 and are beneficial, while the reverse condition is detrimental. — F. D. Heald. 



The experimental morphology of the potato tuber has been taken up 

 again by V6chting.=^^ The French variety '* Marjolin" v^as grown in pots in 

 garden soil. In darkness at a temperature of 6-7" C. few roots, but numer- 

 ous new shoots, are dev^eloped. The latter take the form of small tubers, and 

 never bear the small leaves normally produced in darkness. At a tempera- 

 ture of 25-27'* C (about the optimum for growth) both roots and shoots are 

 produced in large numbers, and the latter all have the form of normal etiolated 

 shoots. As the temperature is decreased below the optimum, more tubers 

 and fewer leaf-bearing shoots are produced, and in the neighborhood of the 

 minimum for growth all the shoots are tuberous. The temperature seems to 

 be directly effective in this response. If new tubers have begun to form in the 

 cold, and then the culture be transferred to the optimum temperature, tuber 

 formation ceases and the development of leafy shoots begins, to continue while 

 the temperature is suitable. A corresponding change from the formation of 

 leafy shoots to that of tuberous ones follows a change of temperature in the 

 o]>posite direction, but leafy shoots started in the cold continue to grow as 

 such at low temj)eratures. However, they change their res[)onse to the grav- 

 ity stimulus entirely ; while at the higher temperature they are* negatively 

 geotropic, at the lower they become positively so. The influence of the 

 amount of water in the soil is almost as important as that of temperature. 

 At a temperature suitable for the production of leafy shoots a culture with 

 little water produces only tubers. When water is added to the soil leafy 

 shoots are developed. In cultures with dry air above the soil, the leaf -bearing 

 shoots creep along the surface of the substratum. The author concludes they 

 are positively hydrotropic. The partial pressure of oxygen is not effective 

 in determining the formation of new tubers or leafy shoots. But with the 

 partial pressure of this gas the roots fail to be provided with the usual hairs. 



— B. E. Livingston. 



CoPELAND^7 has studied the mechanism of the opening and closing 

 movements of stomata in a large number of forms well distributed through- 

 out the plant kingdom. Several methods were resorted to in determining the 

 way in which the various stomata open and close, the main one being the 

 observation of tangential sections of the leaf. Observations of cross and 

 longitudinal sections and of the stomata /;/ situ were also made use of. 

 Unless the methods are at fault (and there seems no reason to believe that 



^^VoCHTiNG, Hermann: Ueber die Keimung der Kartoffelknollen. Bot. Zeit. 

 60: 87-114. /A. j-^. 1902. 



^^Copeland, E. B,, The mechanism of stomata. Annals of Botany 16 : 327'3^4- 

 pi. /J. 1902. 



