STRUCTURAL BOTANY. 53 



either a transformed branch, as in Ampelopsis, or a trans- 

 formed leaf (at least a considerable part of the compound 

 leaf), as in Lathyrns, and finally a changed odd leaflet, as 

 in Yetch and Pea. 



Spines are abortive leaves, or altered stipules. When 

 in the Barberry a leaf-bud is produced in their axil, the 

 spine is held to be nothing but a reduced leaf. In other 

 cases they are petioles, changed after the leaves fall off. 

 In Eobinia we find a pair of spines at the base of the pe- 

 tiole, in place of stipules. "We must distinguish spines, 

 on the one hand, from thorns^ which, originating m axillary 

 buds, are abortive branches, and, on the other hand, from 

 pricldeSj such as those of the Kose and Blackberry, which 

 belong to the epidermis, and may be stripped off with it. 



Stipules are lateral appendages of leaves, always oc- 

 curring in pairs, situated on each side of the base of the 

 leaf-stalk. In a great number of plants they are absent, 

 but their presence is often the characteristic of all the 

 species of an order or tribe. They are various in form, 

 sometimes membranous or scale-like; in other cases, as we 

 have stated above, transfoiTued into spines. They may de- 

 velop on young shoots only, as in the Beech, or in Magno- 

 lia. Xot unfrequently they cohere with each other, or with 

 the base of the petiole. Sometimes a stipule adheres to 

 each side of the base of the leaf-stalk, as in the Rose, 

 Strawberry, and Clover. In the Plane-tree the two sti- 

 pules are free from the base of the leaf -stalk, but cohere 

 by their outer edges, apparently making a single stipule 

 opposite to the leaf. And again it happens, that they are 

 united by both margins, so as to form a sheath around 

 the stem, just above the leaf ; such stipules are said to be 

 inter foliaceous. When interfoliaceous stipules are mem- 

 branous, they bear the name of ochrece^ as in Knot-weeds. 



