BOTANICAL SUBJECTS. 



199 



In the grasses, for instance, we find the stipules adnate to the 

 leaf petiole, and forming 'the vagina, the ligule being evidently 

 no other than the/ree upper ends of the stipules. 



The study of the genus Potamogeton is very interesting and 

 instructive from a stipulary and vaginal point of view, for in its 

 species we find several gradations between the independent stipule, 

 such as we find it in Ficus elastica and the adnate vaginal stipule 

 of grasses. 



For instance, in Potamogeton Rufescens (Fig. 55) we find a 



Peduncle 



Fig. 56. Potamogeton Lucens, Linn. (Syme, pi. 1409.) 

 vagina which is totally independent of the leaf. It envelops the 

 main stem, and evidently served as a protection to the young 

 terminal bud. 



In Potamogeton Lucens (Fig. 56) we find a similar stipule 

 invaginating the peduncle, and, in addition, a second stipule, which 

 appears to belong to the main stem. Here it is evident that these 

 stipules are bud-scales. It is, however, conceivable that, with a 

 little twisting, these two bud-scales might easily become stipules to 

 the leaf, one on each side. 



Fig. 57. Potamogeton heterophyllus, Schreb. (Syme, pi. 1406.) 



