3« 



PARf I. — ORGANOGRAPHY. 



altogether different from ordinary foliage, have also acquired 

 forms which in some instances only remotely resemble those of 

 foliage-leaves. The scales of bulbs like those of the Garlic and 

 Lily, and of bulblets like those of some varieties of the 

 Onion, are leaves surcharged with nutriment laid by to enable 

 the plant to accomplish a vigorous growth during the succeeding 

 season ; the spines into which some of the leaves of the Barberry 

 and all of those of most species of Cactus are changed, subserve 

 protective purposes, effectually defending the plants against 

 browsing mammalia, and the upper leaflets of the common Pea 

 and Vetch, Fig. 127, the entire blade and petiole of Lathyrus 

 aphaca, Fig. 128, and the stipules of Smilax, Fig. 129, are modi- 

 fied into tendrils, and serve the purpose of climbing organs. 



Fig. 127. 



Fig. 128. 



Fig. 129. 



Fig. 130. 



Fig. 127. — Leaf of Vetch with upper leaflets developed into tendrils. 



Fig. 128. — Leaf of Lathyrus aphaca, with^the leaf-blade and petiole developed into a 

 tendril, while the functions of leaf-blade are discharged by the stipules. 



Fig. 129. Leaf of Smilax, with the stipules developed into tendrils. 



Fig. 130. — Leaf of a species of Clematis with petiole serving the function of a climbing 

 organ. 



Sometimes the petioles, while performing the ordinary func- 

 tion of supporting the blade, also become sensitive or irritable 

 to the touch the same as tendrils, and like them perform the 

 functions of climbing organs, as in the Clematis, Fig. 130, and 

 Solanum jasminoides, already referred to, Fig. 18 ; and some- 

 times they are developed into insect traps of various forms, as in 

 the Sundew, Dionsea, the various Pitcher-plants, etc. 



Fig. 131 represents the leaf of the common Sundew. The 

 hairs or tentacles distributed over the surface are each tipped 

 with a pellucid drop of sticky material, by means of which 

 small insects which alight on the leaf are secured ; the tentacles 

 all then bend over upon the insect, and the leaf itself partially 

 rolls inward so as to envelop him, and by means of a secretion 



