36 The Nature and Origin of Stipules. 



The ochrea of palms is doubtless of the same character, though 

 I have not had opportunity to examine its anatomical structui'e. 

 In those species which I have examined morphological^, the case 

 is that of the ochrea associated with a remarkable development 

 of the sheathing petiole. There is no true petiole and the ligule 

 may be seen even a little above the base of the blade on the upper 

 surface of the midrib. From this point the lateral portions may 

 be traced down the margins of the sheath, though dried up and 

 very much torn and broken by the more rapid development of 

 the central tissues, till they unite with those parts which in their 

 development have formed the " ochrea." The degeneration of the 

 sheathing petiole with the probable concomitant formation of a 

 true petiole would give the same conditions as in Polygonum 

 with its typical ochrea. 



The ochreate stipule of Platanus differs little morphologically 

 from the typical ochrea, except in the absence of development of 

 the central-basal portion and the possession of a horizontal limb, 

 but there is no fibro-vascular support for the ligular part and this 

 usually splits, leaving apparently a single stipule opposite the 

 leaf. 



The case of the tendrils of Smilax is one which has occasioned 

 much discussion, but the embryological together with the anatom- 

 ical characters make it sufficiently clear that in Smilax the ten- 

 drils are true stipules found in connection with the sheathing 

 petiole. If a young shoot of Smilax rotundifolia L. be examined, 

 the first leaf (fig. 35) is seen to be of the typical primitive form. 

 In the second (fig. 36), the apical portion has developed into a 

 blade of considerable size and there is a well-marked sheathing 

 petiole. In the third (fig. 37), the true petiole has begun to de- 

 velop, the central-basal portion is degenerating and at the same 

 time the lateral portions have begun to separate, forming rudi- 

 mentary tendrils which in the adult leaves come to considerable 

 length by secondary development in adaptation to their new and 

 unusual function of support. In cross section the bundles of the 

 tendrils are seen to arise as branches of those of the petiole, so 

 that anatomically, as well as embryologically, they answer to true 

 stipules. 



Pastinaca sativa L. (fig. 38) furnishes a good example of the 

 sheathing petiole among the Umbelliferae. The lateral portions are 

 broad and furnished with several vascular bundles parallel with 



