. Cuar. V. CONCLUDING REMARKS. 201 
these filaments are variable in shape, as is so fre- 
quently the case with rudimentary organs; they are 
either cylindrical, or foliaceous, or are deeply furrowed 
on the upper surface. They have not retained any 
vestige of the power of revolving. It is a curious 
fact, that many of these filaments, when foliaceous, 
have on their lower surfaces, dark-coloured glands like 
those on the stipules, which excrete a sweet fluid; so 
that these rudiments have been feebly utilized. 
One other analogous case, though hypothetical, is 
worth giving. Nearly all the species of Lathyrus 
possesses tendrils; but D. nissolia is destitute of them. 
This plant has leaves, which must have struck every 
one with surprise who has noticed them, for they are 
quite unlike those of all common papilionaceous 
plants, and resemble those of a grass. In another 
species, L. aphaca, the tendril, which is not highly 
developed (for it is unbranched, and has no spon- 
taneous revolving-power), replaces the leaves, the 
latter being replaced in function by large stipules. 
Now if we suppose the tendrils of L. aphaca to become 
flattened and foliaceous, like the little rudimentary 
tendrils of the bean, and the large stipules to become 
at the same time reduced in size, from not being any 
longer wanted, we should have the ‘exact counterpart 
of LZ. nissolia, and its curious leaves are at once 
rendered intelligible to us. 
It may be added, as serving to sum up the foregoing 
views on the origin of tendril-bearing plants, that L. 
nissolia is probably descended from a plant which was 
