DEPARTMENT OF BOTANICAL RESEARCH. 63 



be expected. After penetration has been accomplished the further structural 

 modifications of the parasite occur in direct response to the physiological 

 activities of the particular tissues of the host. From the latter the second 

 condition is met, namely, a delayed definitive development of the tissues of the 

 parasite, and great plasticity by which parenchymatous tissues might be modi- 

 fied in many ways toward perfected morphological articulation with the host. 



The Determination of Leaf-temperatures, by Bdith B. Shreve. 



A special form of calorimeter containing turpentine was designed for the 

 purpose of testing the temperatures of leaves. The cup is of thin brass, 

 nickeled and polished, and the jacket is a silvered Dewar vacuum beaker. 

 The cup is suspended near the bottom of the jacket in a wooden ring and is 

 closed by a cover of wood perforated for a thermometer and a stirrer. The 

 opening in the jacket is closed by a plug of cotton wool. When leaves were 

 placed in the turpentine of the calorimeter their temperatures were found by 

 the reduction of the formula A (Sa) (Ta — Tc) =B (Tc — Tb) + C, in 

 which A = weight of leaves, B = weight of turpentine, Sa = specific heat 

 of leaves, ^& = specific heat of turpentine, Ta = original temperature of 

 leaves, Tb = original temperature of turpentine, Tc = final temperature of 

 the mixture, and C is the amount of heat absorbed by the containing vessel. 

 The substitution of known or ascertainable quantities allows the ready 

 calculation of the original temperature of the leaves to within 0.2° F. 



Autonomic Movements of Cylindrical Stems of Opuntia, by Bdith B. Shreve. 



The inception, duration, and character of the movements of maturing 

 stems of Opuntia discovered by Dr. D. T. MacDougal in 1909 was studied 

 by observations and experiments with plantlets of Opuntia versicolor under 

 control conditions and in the open. These movements ensue in young plants 

 20 to 60 cm. in height with such amplitude that the tips of the stems are 

 carried through an arc extending from the ground on one side of the stem 

 over to a similar position on the opposite side. Movements of a similar kind 

 are exhibited by branches of large plants which result in placing these mem- 

 bers in a final position much different from the original one. The movement 

 is influenced by light, but its mechanism has not yet been made out. 



Chemical Effects of Radiant Energy in Plant Processes, by H. A, Spoehr. 



Further studies with ultra-violet light have shown that, contrary to the 

 statements of Usher and Priestly, carbon dioxide, either in gaseous form or 

 when dissolved in water, is not reduced to formaldehyde when exposed to 

 these rays. However, it has been found that formaldehyde is formed when 

 a solution of potassium carbonate containing colloidal platinum and through 

 which carbon dioxide is allowed to pass is exposed to ultra-violet light. The 

 failure to get a reduction of carbon dioxide in the presence of nascent hy- 

 drogen, when this is produced electrolytically, disproves the theory of Stok- 



