The Morphology of Riippia Maritima. 



83 



3. Stem Structures in the Floral Region. 



Three forms coming under the category of stem are found in 

 connection with the production of flowers and fruit: (a) the peduncle, 

 or the stalk of the inflorescence, (using this term in its narrower 

 sense); (b) the rhachis or axis of the inflorescence, which is joined 

 to the apex of the peduncle and bears the sessile flowers; (c) the 

 stipe, a stalk which acquires its full development subsequent to the 

 fertilization of the ovule and bears the mature fruit at some dis- 

 tance from the rhachis. 



These three parts will be considered in order. 



a. Peduncle. 



(Ij General Characters. 



At the time of blooming the peduncle is short, about 2.5 cm., in 

 length, and is raised nearly its whole length verticall}' above the 

 surface of the water. About the time that the pollen is shed 

 and the anthers fall ofl", the peduncle becomes horizontal, floating 

 on the surface of the water. From now on it commences to 

 elongate, presumably b}' simple stretching of its cells, as no merist- 

 ematic regions were found to prove the contrar}'. It elongates 

 until in some cases it attains great length. One specimen I measured 

 was 18.2 cm. long. Elongation takes place whether fruit is matured 

 or not, and the length is apparently just as great in either case. Indeed, 

 the specimen just men- 

 tioned bore no fruit. The 

 average length of the 

 peduncle when no fruit 

 was matured was 5.39 

 cm. The average length 

 in 80 specimens when 

 ovules were matured 

 was 4.9 cm. On the 

 whole, therefore, the 

 average length of the ex- 

 tended peduncle is about 

 5 cm. or about twice that 

 at the time of flowering. 



(2) Anatomical struc- 

 ture. 



In general, the anatom- 

 ical structure of the ped- 

 uncle is very similar to that of the leafy stem (Text-fig. 9; PL VI, 

 fig. 34). The following points, however, are noteworthy : — 



Figure 9. — Cross section of peduncle, showing 



at X the apparently double epidermal cells; 



ep^ epidermis ; la, lacunae ; c, cortex : axb^ axial 



bundle, x 185. 



