488 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Mechanism of Root Curvature.* — From observations made chiefly 

 on Vicia Faba, Mr. Jas. B. Pollock comes to the following general con- 

 clusions. The transmission of the stimulus from the sensitive tip to that 

 part of the root which curves takes place in the cortex, and this may be 

 on either the concave or the. convex side. It is not probable that any 

 part of the transmission takes place through the axial cylinder. The 

 stimulus may be transmitted in the transverse or tangential, as well as 

 in the longitudinal direction. Tl.e mechanism is closely connected with 

 the tissue tensions existing in the organ previously to stimulation. The 

 ordinary tissue tension of roots is the reverse of that in stems : — the 

 outer cortical parenchyme is under positive, the central cylinder under 

 negative tension. Stimulation causes an increase in the tension between 

 the axial cylinder and the cortex on the side which becomes convex, and 

 decreases or reverses the tension between the axial cylinder and the cor- 

 tex on the other side. Not only is the tension between the axial cylin- 

 der and the cortex on the side that becomes concave changed by the 

 stimulus, but the different layers of the cortex itself change in their ten- 

 sile relation to one another. In curving roots the outer layers of the 

 cortex on the concave side are under negative tension in relation to those 

 layers which are more central. In traumatropic curvature (Vicia Faba), 

 the zone of maximum curvature does not coincide with the zone of 

 maximum growth, but is nearer the tip. The cells of the convex half 

 of curved roots contain a larger quantity of water than those of the 

 concave half. 



After carefully examining all the theories that have been advanced 

 to account for the curvatures due to stimulation, the author has come to 

 the conclusion that no one of them is entirely adequate. 



C4) Chemical Chang-es (including' Respiration 

 and Fermentation). 



Transformations of Organic Substances during Germination.f — 

 From experiments made chiefly on Phaseolus, M. G. Andre concludes 

 that the regeneration of insoluble albuminoids takes place at the expense 

 both of asparagin and of the nitrogen of the amide-acids. This takes 

 place concurrently with the absorption of phosphoric acid by the plant. 

 The soluble carbohydrates are apparently, in part at least, oxidised di- 

 rectly in respiration. Starch and the cellulose which can be saccharised 

 by dilute acids at 100° C. decrease progressively from germination until 

 the time when the weight of the plant is greater than that of the seed ; 

 while the amount of cellulose properly so-called (not saccharised by 

 dilute acids) continually increases, this being largely due to the trans- 

 formation of starch. 



Chlorosis of the Vine.:}: — Mr. G. Curtel has investigated the nature 



of the physiological injuries inflicted on the vine by chlorosis. It is 



shown by an evident weakening of the respiratory activity, and a dimi- 



CO 

 nution of the proportion —J* of the gases exchanged ; by the diminution 



and final cessation of assimilation ; and by a very great weakening of 



* Bot. Gazette, xxix. (1900) pp. 1-63 (1 fig.). 



t Comptes Rendus, exxix. (1899) pp. 1262-5; exxx. (1900) pp. 728-311. 



I Op. cit., exxx. (1900) pp. 1074-6. 



