48 CLIMBING PLANTS [CHAP. 



to by Darwinians, and that is transitional 

 structures. Suppose they arose by spontaneous 

 variations, how are we to distinguish between 

 the original stage, the completed alteration, and 

 the half-and-half mean ? Climbing plants afford 

 good illustrations. Clematis climbs by means 

 of the petioles of the leaves, the blades being 

 unaltered ; only the petiole has acquired a 

 sensitiveness to touch, and coils round an object 

 against which it is pressing. Naravelia differs 

 from Clematis in having the leaves with some 

 of the blades in the form of thread-like tendrils 

 but not all. The garden pea is in the same 

 condition, but in Lathyrus Aphaca of the pea 

 family the blades are wanting, the entire leaf 

 being changed. If the half-and-half stage, as 

 of Corydalis claviculata (fig. 14), is to be a 

 " mean," then why is not this always the 

 character of leaf- tendrils ? 



The tendrils of the vine are, as stated, meta- 

 morphosed flowering branches and, as a rule, 

 bear no flower-buds ; but such may soon be 

 found if a vine be searched (fig. 15). And 

 when they do occur, it is easy to see that this 

 " mean " condition is a disadvantage to the 

 plant, as a portion of sensitiveness is lost. The 

 " maximum " or perfect and complete tendril is 

 obviously the most efficient. Mr Reid recog- 

 nises the hereditary character of tendrils and 

 that the plants "use" them. Though no one 



