The Nature and Origin of Stipules. 35 



what should be regarded as its ancestral development, and a con- 

 dition approaching that which occurs in grasses is found. Po- 

 tamogeton crispus L. is one of our species which will serve well for 

 an illustration. The first leaves do not develop a blade, but the 

 lateral and central-basal portions are well developed. In the adult 

 leaves there is present a true sheathing petiole (fig. 29). The 

 fibro-vascular bundles of the central-basal portion pass into the 

 blade, giving off tangentially, at the point of transition from 

 sheath to blade, the bundles of the ligular part of the stipule. 

 The bundles of the lateral portions do not in this case curve about 

 to join those entering the blade but are prolonged upward, re- 

 maining parallel and supplying the lateral portions of the stipule 

 with supporting tissue directly. In Althenia filiformis Petit. 

 (fig. 30), the conditions are more primitive in the larger relative 

 development of the lateral and central-basal portions. In JRuppia 

 the ligule is not developed, and the tips of the lateral portions 

 are free as in ordinary adnate stipules. 



The condition found in Potamogeton is almost exactly repeated 

 in Polygonella articulata (L.) Meisn. (fig. 31). The ochrea is 

 cylindrical, surrounding the stem. The central-basal portion is 

 long and narrow, bearing at its apex the terete lamina which is 

 deciduous before flowering. The lateral portions form the prin- 

 cipal part of the sheath, are parallel veined with a few anastomos- 

 ing bundles and are prolonged above the central-basal portion, 

 growing in along the ridge between it and the lamina. This middle 

 portion shows its origin by a deep median sinus and receives its 

 bundles typically as tangential branches from those entering the 

 lamina. We do not have then in Polygonella a typical ochrea as it 

 occurs in Rumex and Polygonum, where, because of the small de- 

 velopment of the central-basal portion, the sheathing petiole is 

 very short or almost wholly wanting. The lamina, being of much 

 greater importance than in Polygonella, receives all the bundles of 

 the leaf-trace. They are more or less abruptly deflected into the 

 true petiole, generally developed in these genera, according to the 

 degree of degeneration of the central-basal portion. The lateral 

 portions receive their supporting bundles as branches of the lateral 

 ones of the leaf-trace. In Polygonum sagittatum L. (fig. 32), the 

 marginal tissues do not extend across the petiole and we have a 

 stipule opposite the leaf. In Rumex crispus L. (fig. 33) and 

 Polygonum Virginianum L. (fig. 34), the ochrea is complete and 

 the axillary parts receive the tjpical tangential bundles. 



