The Morphology of Ruppia Maritima. 



153 



dermatogen, as he asseits, I was not able to determine. The whole 

 group is supposed to represent the vestiges of the primary root 

 (Murbeck, 1902, p. 18; Wille, 1883, p. 4), which develops only to 

 this rudimentar}^ degree, and never functions. 



The First Adventitious Root. At about the period when the coty- 

 ledon and epicotyl have become quite distinct in outline, the form- 

 ation of an adventitious root occurs near the base of the epicotyl. 

 This grows rapidly, forming a noticeable protuberance (PL XIV, 

 figs. 112, 113), and in the mature embryo (Text-lig. 28) may be 

 seen pointing almost directly upward, or nearly at right angles to 

 the position of the cotyledon. 



The distribution of the meristematic regions at the tip of this 

 adventitious root is not as clearly marked as in the roots of the 

 mature plant. It will be recalled that the roots of the mature plant, 

 as in Zannichellia, contain at their tip four distinct meristematic 

 regions, representing the initial areas of calyptrogen, dermatogen, 

 periblem and plerome. 



In the young adventitious root of the embryo an interesting point 

 is the division of the epidermis of the hypocotyl, immediately over 

 the young developing root, by 

 periclinal walls, apparently to 

 form root cap. These divisions 

 continue, and anticlinal as well 

 as periclinal occur. This is a very 

 different condition from that in 

 the roots of the mature plant. 



Whether the dermatogen and 

 periblem are each also here re- 

 presented by a single layer at the 

 apex of the growing-point would 

 be impossible to assert definitely, 

 on account of the irregularity of 



the cells, but such seems to be 



r. ,. ,™ ^^ „„. rT Fiffure 29. — Lohsritudlnal section 



often the case (Text-fig. 29). How- through apex of adventitious root o£ 



ever, some embryos show only nearly mature embryo ; showing pi., 



one layer for both dermatogen plerome, ^, dermatogen, and periclinal 



1 n r- J divisions initiating deveJopment oi 



and plerome. as CampbeU finds calyptrogen, cat. x B30. 



most usual in the primary root 



of Zannichelha (Campbell, 1897, p. 51). The plerome is pretty 

 clearly marked (Text-fig. 29), but also does not have as definite a 

 point of origin as in the roots of the mature plant. 



