Ciiap. 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 L. 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. aphaea 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 L. 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 



