The Morphology of Ruppia Maritima. 85 



(3) Coiling of the peduncle. 



Sooner or later the peduncle becomes spirally coiled, drawing 

 the fruit, if any is matured, below the surface of the water. Some 

 individuals exhibit this characteristic more markedly than others. 

 Often, in fact, the peduncle is fairly straight. In case the coiling 

 takes place, it is due to the cells on that side of the peduncle which 

 will form the outer side of the spiral becoming longer than those 

 on the inner side. This difference in length was ascertained in 

 several specimens b}'' actual measurement of the cells. Such cur- 

 vatures as this occurring in plants are most often, as Strasburger 

 (1908, p. 269) has explained, due in like manner to unequal growth. 



b) Rhachis. 



Here the internal structure is practically the same as in the ped- 

 uncle. No appreciable elongation takes place as in the peduncle, 

 and, therefore, the tracheae are not disorganized to such an extent. 

 At the point of attachment of the stamens the rhachis is practically 

 triangular in outline (PL III, fig. 11). The single axial vascular 

 bundle sends a branch to each stamen and to each of the four 

 pistils of a flower (PL III, fig. 12). This axial vascular region 

 terminates with the branch sent to the uppermost stamen (PL III, 

 fig. 12), the most distal member of the inflorescence, and does not 

 therefore have a blind ending at the end of the rhachis. 



The termination of the rhachis is simply a rounded knob (PL III, 

 fig. 12). 



All through the rhachis, in the interior as well as in the epidermal 

 tissue, the " secretion " cells are abundant. 



c) Stipe. 



Although the pistils are termed sessile, and correctly so from a 

 macroscopic standpoint, early in their development, before fertilization 

 (PL III, fig. 12), considerable tissue is formed between the ovule 

 and the rhachis by a region which remains meristematic for some 

 time. At length the cell division ceases, and the cells stretch out, 

 forming a stalk of considerable length, having at its end the mature 

 fruit (PL IV, fig. 13). This stipal development is correlative; when 

 no fruit is developed, the stipe is also wanting. 



PL IV, fig. 14, which shows the secretion cells in the epidermis 

 of the stipe, represents a stage when the cells are still quite young 

 and short. 



In its internal structure the stipe reveals no marked differences 

 from the stem (PL IV, fig. 15). As in the peduncle, the cortical 

 bundles are lacking. The lacunae are less pronounced than in the 

 peduncle. The apparently halved epidermal cells occasionally appear, 



