252 



BOTANY 



PART I 



the other harul, determine the primary inception and point of develop- 

 ment of the haustoria of Cuscuta. 



Mechanical influences, probably stresses at the jjlaces of de- 

 velopment of lateral roots lead to the lateral roots developing only 

 on the convex side of a curved main root (Fig. 207). Chemical 

 STIMULI have doubtless great significance in organogenesis ; proceed- 

 ing from foreign organisms, they determine the formation of GALLS (^*^). 

 The development of adventitious formations is especially induced 

 by MUTILATION of plants ; the same effect may result when the organs 



or growing points though unin- 

 jured become functionless. New 

 FORMATIONS are in this manner 

 produced at points from which 

 they would never have arisen on 

 the uninjured plants. In the case 

 of Pelargoniums, Willows, and 

 many other plants, it is possible 

 to induce the formation of roots 

 wherever the shoots are cut. In 

 other plants, however, there seem 

 to be certain preferred places, 

 such as the older nodes, from 

 whicli, under the same circum- 

 ^ stances, roots develop. In like 

 manner new shoots will appear 

 in the place of others that have 

 been removed. In the develop- 

 ment OF NEW FORMATIONS ON A 

 MUTILATED PLANT THOSE VERY 



Fig. 207.— Young plant of Lupine, the main root of ORGANS ARISE, OF WHICH THE 



which has become curved. The lateral roots PLANT HAS BEEN DEPRIVED, 



have arisen on the convex faces of the curves, RootleSS shootS develop first of 

 and act as stays. , , -n i ^ 



all new roots. Koots and root- 

 stocks deprived of their shoots form first new shoots. 



While the apical and the intercalary growing points are specially 

 adapted for such regenerative processes, the same power may also be 

 possessed by fully grown parenchymatous cells ; in some plants this 

 is very marked. 



The polarity of the body of the plant is exhibited in a striking 

 manner in the phenomena of regeneration. Every small isolated 

 ])ortion of the stem or root exhibits from internal causes (p. 253) a 

 distinction of base and apex which was not apparent Avhen it formed 

 a part of the intact plant. Each portion of stem produces new shoots 

 at its apical end (shoot pole) and new roots at its basal end (root pole). 

 Each portion of root forms shoots at the end which was nearest to 

 the stem and roots at the end directed to the root-apex. A similar 



