28o BOTANICAL GAZETTE [april 



here in high degree, and are regarded by Witte^^ as of advantage in checking 

 transpiration. The alfvar was very fully treated from this standpoint some years 

 ago by Grevillius. Some plants commonly herbs here become half-shrubs, 

 e. g., Gypsophila jastigiata. There is an excellent study made of the underground 

 organs, which are frequently neglected.— H. C. Cowles, 



Lateral roots.— Noedhausen has studied the direction and growth of lateral 

 roots under the influence of external factors, particularly those which arise from 

 the removal of portions of the main root or its wounding. '" It is well known that 

 when a millimeter or less of the primar}' root is cut off, regeneration of the tip 

 occurs; but when larger portions are removed, one or more of the lateral roots 

 change their angle with the main axis, as it were to substitute themselves for it. 

 NoRDHArsEN Can only say, as one result of his studies, that this reaction on the 

 part of the lateral roots is ''dependent upon the intensity and quahty of internal 

 conditions which bear more or less relation to the needs of the plant," which of 

 course is an empty form of words. It was already known that decapitation within 

 the growth zone results in a very active substitution response. If the cutting 

 exceeds this, however, whether much or little, says Nordhausen, this response is 

 minimal or wanting, provided a rather long piece of the primary root remains; 

 but shortening the stump beyond a certain amount again increases the response. 

 The alteration of the angle of the substitute roots with the main axis rests, con- 

 trary to the conclusions of Bruck and Czapek, upon both geotropic and autotropic 

 factors, of which the former is determinative. This substitution of lateral roots 

 is mdependent of actual wounding, since it can be brought about by merely 

 checking the growth, especially of the main axis. A partial response follows 

 even without disturbance or operation on the growing point, if certain tracts 

 within the central cylinder (not only in the phloem but especially in the xylem) 

 are interrupted by lateral wounding. The disturbance of nutrition here plays 

 only a subordinate role. Nordhausen a^ees with McCalltjm in assuming 



) 



gulating 



in 



intact plants. Certain roots (Lupinus, Phaseolus) respond to a temporar>' past 

 reduction in the water supply by altering the angle of lateral roots, which at the 

 time of the difTiculty had not even appeared, though when they develop they are 

 under normal conditions. Lateral wounding of the main root leading to direct 

 or indirect affection of the pericambium, even before the lateral roots become ns- 

 xble, produces a traumatropic deviation of these from the wounded side. The 

 transmission of the excitation, easier in the acropetal than the basipetal direction, 

 may produce sympathetic response of more distant lateral roots. 



i he influence of curvature of the main root upon the form and lateral deviadon 

 ot the side roots, determined by Noll and explained ( ?) as morphaesthesia, is 

 ^^^^^^fOT^g to Nordhausen, to changes in the tension of the central qlindcT, 



'J WiTTE, H., Till de Svenska alfvarvaxternas ekologi. pp.119. Upsala. i9'^- 

 A.J'J^T^^'^'^^^''' •^•' ^^^"^ Richtung und Wachstum der Seitenwurzelen unter 

 em L.nfluss ausserer und innerer Faktoren. Jahrb. Wiss. Bot. 44:557-634- ipo?- 



