FOLIAGE AND SCALE LEAVES. 6$ 



nettle. Emergences are also found in many eases, especially where 

 the veins project on the lower side. (For Sheath, cf. p. 154.) 



"We next come to the consideration of Stipules (cf. p. 53). 

 These are not always of the same nature. In the pansy, for 

 example, they are extremely large and foliaceous or leaf-like, 

 and very likely correspond to the lateral lobes of a ternately- 

 parted sessile leaf. The same, or something similar, appears to 

 be true of many foliaceous stipules, as perhaps in the case of 

 the bean. pea. cVr., where they look like a basal pair of leaflet.-. 

 In fact, they may be the sole organs for performance of the leaf 

 functions, as far as nutrition is concerned. The wild-peas, be- 

 longing to the genus Lathyrus, illustrate in a very interesting 

 way the mutations to which the regions of the leaf are liable. 

 There are several British species. In one of these, the black 

 pea (Lathyrus niger), the midrib of the pinnate leaf ends in a 

 point ; there are fair-sized stipules, and several pairs of leaflets. 

 Another species, the blue marsh-pea (L. palustris), has leaves 

 tendrilled at the ends, larger stipules, and fewer leaflets. The 

 leaves of the meadow-pea (L. pratensis) possess only one pair of 

 leaflets and more tendrils. Lastly, in the yellow pea (L. Aphaca). 

 the whole leaf is converted into a tendril, with the exception of 

 the stipules, which are extremely large. Curiously enough, there 

 is one species of Lathyrus, the grass-pea (L. Nissolia), in which 

 neither leaflets nor tendrils are present, and the stipules are verv 

 small. The leaf -axes are here converted into phyllodes shaped 

 like grass leaves. This condition is led up to by one or two other 

 species where the petiole is winged. 



Many stipules are membranous, and very unlike the foliaceous 

 examples already mentioned ; and also they are not necessarily 

 in the form of two free expansions, but may be united in various 

 ways. Examine, for instance, a rose leaf, in illustration of the 

 latter point. The petiole is sheathing at the base and bordered 

 by a green wing on either side, which ends in a pointed lobe some 

 distance from the first pair of leaflets. These two wing-like pieces 

 are called adnaie stipules, from the idea that they represent two 

 of these structures adherent to the petiole. Such stipules are 

 probably simply surviving bits of a once more extended wing. 

 In many roses the adnate stipules are much smaller and not 

 green. This, is also the case in clover. A pair of stipules may 

 unite in the leaf-axil to form an axillary stipule. Something 

 akin to this is found in a membranous ligule, which in grasses 

 projects from the upper side at the junction of sheath and lamina 

 (fig. 10). Indeed, this and many undoubted stipular structures 

 appear to belong to the leaf-sheath. Two stipules may also be 

 united into an opposite stipule, placed on the oj>posite side of the 



