SUPPLEMENT 147 



499, 11. 23-7, for [The mechanics . . . 1903 b).] read This proves that these 

 tendrils also possess a certain degree of dorsiventrality. 



Further, in the tendrils studied by FITTING (1903 a), curvatures followed 

 wounding, not in all species, but always in the same direction. These curva- 

 tures may be induced by decapitation or by incisions as deep as the central 

 cylinder. It is worth noting that, after basal incision, inrolling still takes 

 place at the apex, and that the transmission of the stimulus is unusually rapid 

 and far-reaching. 



500. Lecture XXXIX is XXXVIII of the 2nd German Edition. 



1. 10, for NYCTITROPISM read NYCTINASTIC MOVEMENTS 



1. 21, for speaking generally, we may employ the terms read we may 

 employ the more general terms 



1. 44 P. 502, 1. 47, for These same . . . decreased, read Since in nature 

 photonastic and thermonastic movements take place especially in relation to 

 the alternation of night and day, we may also speak of them collectively 

 as ' nyctinastic movements '. Under this term may be also included the 

 less important reactions which result from changes in degree of moisture 

 ' hydronastic movements '. 



The reason why we associate nyctinastic with haptotropic movements 

 is that the mechanics of the former often entirely correspond to those dis- 

 covered in tendrils, and this is true of all nyctinastic movements which are 

 carried out by growth agency. We may commence with the thermonastic 

 movements seen in many flowers. 



If a spring flower (such as a tulip or crocus) be subjected to increased 

 temperature, e.g. in a warm room, more vigorous growth at once takes place 

 on the upper sides of the perianth leaves, and so the flower opens. Indeed 

 the upper sides become more or less convex, and the flower opens more or less 

 according to the height of the temperature. Curvatures visible to the naked 

 eye appear in the crocus even when the temperature has been raised only 

 half a degree. If the temperature be raised considerably (e.g. io-20) the 

 curvature does not remain constant when the temperature is maintained at 

 that height ; on the contrary, an incurving or closing follows. This occurs 

 in the tulip within two hours, but later in the crocus. This closing movement, 

 however, by no means brings the flower back once more to the state in which 

 it was when in the cold ; the leaves take up a new position of equilibrium, 

 corresponding to the increased temperature. If the temperature has been 

 slowly raised the opening takes place more slowly, and the supra-curvature 

 is not so great. 



In endeavouring to elucidate the cause of the curvature and recurvature 

 we must determine the growth on the upper and under sides of the perianth 

 leaves during these movements by the aid of marks whose distances apart 

 have been measured by a micrometer. The marks are made on the basal part 

 of the leaf, for it is there that the most vigorous growth and greatest curvature 

 take place. The results of such measurements are expressed graphically in 

 Fig. 157 a. We see that in the tulip, as soon as the rise in temperature begins 

 to operate, growth sets in on the upper side of the leaf, and it shows a very 

 considerable extension (about 7 per cent.) in the course of one hour. At the 

 same time the under side decreases in length, while the median region shows 

 growth which is markedly more rapid both as contrasted with that occurring 

 at 7-5 and that later on at 26. In the second hour the under side of the 

 perianth, however, begins to grow with considerable acceleration in the median 

 region, and thus the backward curvature is brought about. A comparison 

 of Figs. 154 and 157 a shows at once how remarkably similar this curving 

 process is in its mechanics to that observed in tendrils. The only difference 

 is that in the tulip the reverse action on the under side begins before growth 



K 2 



