170 BUDS AND STIPULES 



late, with the petiole transformed into a grooved sheath, 

 membranous at the margin right up to the base of the 

 lamina ; the second and third leaves have a similar but 

 shorter sheath and oblong lamina (fig. 292, a) ; the fourth 

 leaf is oblong or oblanceolate, with the membranous 

 sheath partly separated from the petiole, and forming 

 stipules still adnate for the greater part of their length 

 (fig. 292, &); the fifth and sixth leaves are similar, with 

 shorter petioles and shorter, but more evident, stipules 

 (fig. 292, c). Here, then, we have in the bud a gradual 

 transition from leaves wholly reduced to sheaths to those 

 with a lamina and a sheath, then to those with a lamina, 

 petiole and stipules, the latter being adnate to the 

 petiole for a greater or less part of their length. 



Several other species of Rosacece, belonging to various 

 genera (C-ratcegus, Geum, Pyrus, Potentilla, &c.), present 

 us with cases of polymorphic stipules. 



Hlxochorda Alberti, a member of a small Central 

 Asiatic genus, is a very curious case. The lower leaves 

 have well-formed stipules at the base of the leaf-stalk 

 (see ante, fig. 53, p. 39). Gradually the base of the leaf- 

 blade elongates and the true petiole shortens, so that 

 the stipules are attached higher and higher up, nearer 

 and nearer to the blade. The upper leaves have a tooth 

 at the base, which, however, is very variable, and often 

 absent on one side. Finally, the uppermost leaves 

 generally show no trace of stipules or teeth. 



As a general rule the two stipules of the same leaf 



