42 The Nature and Origin of Stipules. 



suiting in the adnate stipules characteristic of so man}- genera and 

 species of the family. Agrimonia striata Michx.,in the develop- 

 ment of its subterranean buds in the spring, presents an excellent 

 series of embryonic leaf-forms. The lower ones are all simple 

 sheathing scales completely surrounding the stem at their inser- 

 tion. Not until the eleventh leaf (fig. 53), which is three-toothed 

 at the apex, does the differentiation of parts begin. The central 

 tooth is the beginning of the blade with its petiole ; the lateral 

 portions with their tips now free are the stipules. To sa} r that 

 they are " adnate" indicates only that they retain their primitive 

 connection with the central-basal portion. In the twelfth leaf 

 (fig. 54), there has been some basal degeneration, as shown by the 

 lower point at which the three main bundles of the leaf converge 

 and the lower position of the zigzag plexus of the stipular veins. 

 The free tips, on the other hand, have increased in size and a small 

 blade supported by a petiole is present in consequence of the de- 

 velopment of the central tooth. The fifteenth leaf (fig. 55) shows 

 a stronger development of all the parts, and a branch of the main 

 stipular bundle is seen to pass up the petiole. The adult form is 

 attained in the seventeenth leaf (fig. 56). In it some further 

 basal degeneration has taken place, but the adnation of the sti- 

 pules is still very prominent. 



Prunus Gerasus L. gives a very good morphological sei*ies,but 

 the venation is obscure. A view of the several forms can be had 

 by an examination of the tenth, thirteenth, fifteenth, sixteenth 

 and seventeenth leaves (figs. 57-61). They show the transition 

 from the simple primitive scale to the mature condition in which 

 the stipules are rendered entirely free. The series is similar in 

 Rubus occidentalis L., Pyrus Malus L. and Pyrus communis L. 

 In Rubus villosus Ait. (figs. 62-66), the basal degeneration is not 

 carried quite so far and the stipules in the adult leaf-forms re- 

 main adnate for some distance from the base of the leaf. The 

 tips of the stipules have taken a larger comparative development 

 than in Agrimonia. Anatomically, however, Rubus villosus Ait. 

 resembles the latter in having a vein which enters the petiole, 

 neighboring to the main stipular bundle much as in Viola obliqua 

 Hill (fig. 18). The venation in Pyrus Malus L. (fig. 67) is still 

 more like that in Agrimonia. 



The stipules of Fragaria and Rosa show the highest degree of 

 adnation and little, if any, basal degeneration seems to have taken 



