Cucurbita maxima and C. Pepo. 185 



these bands of growth " travel round the tendril and suc- 

 cessively bow each part to the opposite side," and in this lies 

 the essential part of the true explanation of the movement. 



As already indicated, the figure described is not one of regu- 

 lar progression through successive points of an ellipse or other 

 figure, but the tendril tip may change its direction very 

 abruptly, often exactly retracing the path just passed over, or 

 the change of direction may be less abrupt (fig. 2). This indi- 

 cates in the first place, that the band of growth does not pass 

 regularly through successive points in the circumference of the 

 tendril, but that it changes its position without regard to order 

 of succession. But it also appears from the figure obtained, 

 that while revolving in this irregular manner, the total dex- 

 trorse and sinistrorse movements are practically equal. 



An examination of the histological elements of the ten- 

 dril as exhibited in cross section, together with the well de- 

 fined relation of the different tissues with reference to ten- 

 sion, suggested that the true explanation of the movement was 

 to be found in the vibrogenic tissue. But it appears (fig. 3) 

 that these bands are three in number, two being lateral and 

 one superior, the latter passing along the upper side of the 

 tendril. If, therefore, they were the true source of the move- 

 ment as described in fig. 2, then the lines traced must be devel- 

 oped as follows : 



We must conceive that, while the parenchyma tissue grows 

 most rapidly, and therefore exerts a determining influence in 

 the circumnutation, the collenchymaand wood tissues of slower 

 growth must also produce a secondary influence which will mod- 

 ify the direction determined by the vibrogen, and thus produce 

 a resultant motion. Thus, line 1-2 (fig. 2) would result from 

 excess of growth in V or in collenchyma a, a' (fig. 3). But at 

 2, the direction of movement is reversed, and back to 3 it must 

 be the resultant of excess of growth in b'\ plus a weaker growth 

 in collenchyma a" . From 3^L, vibrogen V exerts a superior 

 influence, while from 4-5, b has again the ascendancy overall 

 the other tissue and the motion is therefore directly lateral. 

 And so on for the other lines traversed, each change of direc- 

 tion being the direct expression of superior energy in one of 

 the vibrogenic bundles, or the resultant of growth in both 

 vibrogen and collenchyma, the excess of growth always being 

 in one of the vibrogen bundles. But this result might be pro- 

 duced without the energy being specially localized at b, b\ b'\ 

 The band of growth might pass through various points of the 

 parenchyma tissue at c, c', c", and thus cause the tendril to bow 

 in various directions as explained by Sachs and Darwin. If, 

 however, the vibrogen tissue exerts a preponderating influence, 

 then, since two bands are lateral and one superior, the figure 



