Feb. 1902.] BOTANICAL SOCIETY OF EDINBURGH 183 



bolic inertia that the response to contact appears imme- 

 diate. On the other hand, the tendrils of the AiiqKlidece, 

 with relatively little irritability, display mucli anabolic 

 inertia, the latent period lasting for two hours or more. 



Cases of physiological insusceptibility appear in relation 

 to particular amounts of stimulus. Thus, while a single 

 light touch elicits a response iii Mimosa, for Liomea it has 

 to be repeated, i.e. a kind of double impact is necessary, 

 according to Maefarlane. Drosera, on the other hand, 

 exhibits a refractory period, inasmuch as the efficient 

 stimulus is a continued series of such impacts, i.e. a 

 pressure ; while in tendrils, according to ri'effer, the 

 stimulus is contact with a rough surface, i.e. a series of 

 impacts simultaneously applied at discrete points of the 

 sensitive organ. 



Injury. — Cases of traumatic stimulation are instructive 

 both on account of the varied manifestation of irritability 

 and of the great range in the time value of tlie latent 

 period. This, as we find, may vary from a few seconds to 

 as much as a week, and in some cases may be artificially 

 prolonged to eight days. 



If we take fertilisation as a case of stimulation (Pfeffer, 

 " Physiology," p. 55), we may regard it as of a chemico-vital 

 and traumatic character. Thus, as the spermatozoid breaks 

 the continuity of the plasmatic membrane, and ploughs its 

 way through the cytoplasm, we find as reaction to the 

 traumatic stimulus the formation of a protective cell-wall 

 on the egg. This takes place after a period of anabolic 

 inertia varying from ten minutes in Fueus (Farmer and 

 Williams, "Phil. Trans. Eoy. Soc," 1898, p. 625) to a few 

 hours in other forms. 



Again, a cell membrane may appear around a plasmo- 

 lysed protoplast after fifteen minutes — or more — period 

 of anabolic inertia (Pfeffer, "Physiology," p. 483). 



Injury to the maize epidermis stimulates protoplasmic 

 streaming after fifteen minutes to an hour (Detnier, 

 "Physiology," p. 420). Lateral injury to the root apex 

 induces traumatropic curvature and regeneration of the 

 root tip after a latent period of an hour or so (Spalding, 

 " Annals of Botany," viii. p. 423). By encasing the root in 

 a plaster-cast, or lowering the temperature, the curvature is 



