ANOMALOUS FORMS OF LEAVES.—SPINES. 185 
Stipules, as we have already noticed, are not always present 
in plants, but their presence or absence in any particular plant 
is always constant, and although the appearance and arrange- 
ment of them also vary in different plants, they are always uni- 
form in those of the same species, and even, in some cases, 
throughout entire natural orders, and thus they frequently 
supply important distinctive characters in such plants and 
orders. Thus the plants of the Loganiacez are distinguished 
from those of the allied order Apocynacez by possessing inter- 
petiolar stipules ; and the plants of the Polygonacez usually 
from those of allied orders by intrafoliaceous stipules. 
Stipules are very rare in Monocotyledons, except the ligule 
is to be considered as analogous to them. The only orders 
of Monocotyledons in which they undoubtedly occur are the 
Naiadacez and Araceze. They are altogether absent in Cor- 
mophytes. 
7. ANOMALOUS FORMS OF LEAVES. 
We have already seen that the branches of a stem sometimes 
acquire an irregular development, and take the form of Spmes 
or Tendrils (pages 107 and 108). In the same manner the parts 
of a leaf may assume similar modifications, as well as some others 
still more remarkable, which we now proceed to describe. 
Fic. 383. Fie. 384. 
Fig. 383. A portion of a branch of the Barberry (Ber beris vulgaris), bearing 
spiny leaves. The upper leaf is composed entirely of hardened veins, 
without any parenchyma between them, /ig. 384, A portion of a branch 
of the Gooseberry (Ribes Grossularia). jf, 7. Scars of former leaves, with 
buds in their axils. c. Spine produced from the pulvinus. 
Spines of Leqves.—Any part of the leaf may exhibit a spiny 
character owing to the non-development or diminution of paren- 
chyma, and the hardening of the veins. Thus,—I1st, in the 
Holly (fig. 823) and many Thistles (jig. 283), the veins project 
