§3] 



TKAUMATEOPISM 



385 



ing appeared as a small, dark spot on one side of the radicle. 

 The seedlings were then suspended in a moist chamber, over 

 water, and at a temperature of 14.4° C. After 24 hours almost 

 all of the radicles showed a marked curvature from the 

 wounded side. Other means can be used to produce this 

 result : a thin slice cut off obliquely from the tip of the radicle, 

 a drop of shellac, of copper sulphate, of potassium. hydrate, or 

 steam at about 95° C. (Spaulding) — in general, any agent 

 which irritates strongly without killing. 



Concerning the place on the root where the injury must be 

 made in order that a response should appear, Spaulding finds 

 that if the branding is made further from 

 the apex than 1.5 mm. no traumatic curva- 

 ture will occur ; or if an oblique cut at the 

 apex should not involve the growing root tip, 

 as at ab, Fig. 104, it is without effect. So 

 it seems that the pro- 

 liferating root tip is 

 the sensitive part. 



The point of maxi- 

 mum curvature is, how- 

 ever, not at the root tip. 



but lies in the region 



6 



Fig. 104. — Diagram 

 showing the rela- 

 tions of the root 

 tip, r.t, and the 

 root cap, r.c. ; a, &, 

 line of a cut which 

 involves only the 

 root cap. 



Fig. 105.— Median longi- 

 tudinal section through 

 a, gypsum cast, 6, sur- 

 rounding and repress- 

 ing a root of Vicia f aha. 

 Natural size. (From 

 Pfeffeb, '93.) 



2c 



of most rapid growth. 

 The length of time 

 elapsing between injury and response 

 varies with the species and with the tem- 

 perature. Thus, at a temperature of 18° C. 

 the curvature begins in from 45 to 55 

 minutes, and reaches a maximum within 

 24 hours (Wiesnee). 



The long, latent period and the slowness 

 of complete response give an insight into 

 the reason for this separation of the per- 

 ceiving and responding zones. During the 

 latent period the irritated tissue is be- 

 coming stretching tissue through the im- 

 bibition of water, while the root tip is 

 becoming generated in advance, leaving 



