476 BROOKLYN BOTANIC GARDEN MEMOIRS 



by the production of mechanical tissue would seem to be similar to 

 that induced by other irritable phenomenona. In the formation of 

 the spirals in tendrils there is considerable stress to be overcome and 

 the constantly increasing weight of the various members of the plant, 

 such as is associated with the development of foliage, fruit, etc., 

 together with the effects of rain, swaying movements due to wind, is 

 most admirably met by the production of mechanical tissues. These 

 additional strains are taken care of by the same type of response as that 

 induced by the stretching of plants with weights. Since the leaves of 

 plants appear to be quite sensitive to contact it is readily conceivable 

 how the more specialized haptotropistic responses to contact exempli- 

 fied by tendrils could readily be evolved from simple contact irritability. 

 There are, however, a large class including various types of reaction 

 phenomena which do not fall under tropistic, nastic and taxic responses. 

 These are the so-called wound reactions — traumatotaxis (reaction of 

 cell nucleus). Traumatotropisms, illustrated by decapitated root, and 

 positive galvanic currents on roots, are apparently direct responses to 

 wound stimuli, as probably are the reactions first observed by Darwin 

 resulting from the attachment of different substances to the root tip. 

 In wound reactions, however, contact is involved to a greater or less 

 extent, and more or less injury and abnormal conditions are associated 

 with tWs class of phenomena. Most of the responses following wounds 

 are local in their effect, although the organism as a whole may be 

 affected even from relative insignificant mechanical injuries, as shown 

 by the modification in the developments and functions of the several 

 organs in mutilated plants. 



Representative types of this class are seen in the various accelerated 

 growths produced by insects, fungi, bacteria, mechanical injuries, etc., 

 and generally the reaction continues long after the primary or excitory 

 cause has disappeared. Local accelerated growths, however, do 

 not always follow as a result of the intrusion of pathogenic organism 

 inasmuch as the nature of the response is determined to a large extent 

 by the character of the tissue affected. For example, eel-worm 

 infestation of roots may give rise to galls, whereas on stems such 

 a response may not necessarily follow and even on roots these reactions 

 differ. In many so-called wound reactions the degree of response is 

 disproportionate to the stimulus responsible for the same. This is 

 illustrated by feeble lightning discharges on trees, in which case the 

 stimulus (lightning causing burning) lasts but a few thousandths of a 

 second. The reaction, however, to such insignificant injury — often 

 hardly perceptible and characterized by the destruction of a few 

 cambium cells, may manifest itself for years in an accelerated growth 

 of the annular rings adjacent to the injury. The flow of tissue in 



