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 tnird 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 formiug 

 stipules still adnate for the greater part of their length 

 (fig. 292, b) ; 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 Rosacea 1 , belonging to various 

 genera (Crataegus, Geum, Pyrus, Potentilla, &c), present 

 us with cases of polymorphic stipules. 



Exochorda 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 



