HOME PLANTS AND THEIR WAYS. 15 



fore, but will bend to the near side. Now the old move- 

 ment, caused by the left side growing quickest, will come 

 in again, to be followed by the near side growing quick- 

 est. Thus, by a regular succession of growth on all the 

 sides, one after another, the swinging-round movement is 

 produced, and by a continuation of this action, as I have 

 explained, the twining movement is produced. 



10. I have spoken as if the question of how plants twine 

 were a completely solved problem, and in a certain sense it 

 is so. I think that the explanation which I have given will 

 remain as the fundamental statement of the case. But 

 there is still much to be made out. We do not in the least 

 know why every single hop-plant in a field twines like a 

 left-handed screw, while every single plant in a row of 

 beans twines the other way ; nor why in some rare instances 

 a species is divided, like the human race, into right- and 

 left-handed individuals, some twining like a lei't-handed, 

 others like a right-handed screw. Or, again, why some 

 very few plants will twine half-way up a stick in one direc- 

 tion, and then reverse the spiral and wind the other way. 

 Nor, though we know that in all these plants the twining 

 is caused by the change in the region of quickest growth, 

 have we any idea what causes this change of growth. 



Francis Darwin. 



HOOK-CUMBERS. 



1. The common bramble climbs or scrambles up through 

 thick uuderwood, being assisted by the recurved spines 

 which allow the rapidly growing shoot to creep upward as 

 it lengthens, but prevent it from slipping backward again ; 

 the common goose-grass [Galium) also climbs in this way, 

 sticking like a burr to the side of a hedge-row up which it 

 climbs. Most country boys will remember having taken 



