146 



Till MARATTIALKS 



ruption, and it is quite impossible to say just exactly where the point of junction is. 

 In Angiopteris elongated tannin cells, which stain very strongly, accompany the 

 vascular bundle, both in the rout and cotyledon; bur these are either entirely wanting 

 or bur slightly developed in Marattia and are quite absent from the young sporophyte 

 at this stage in the other genera. In the relation of the primary root and leaf, there- 

 fore, the embryo of the young sporophyte in the Marattiaceae shows a most striking 

 resemblance to the condition found in Ophioglossum moluccanum. 1 he cotyledon, 

 as. in Ophioglossum, is not to be looked upon as an appendage of the stem, but as an 

 organ sui generis. 



Almost as soon as the second leaf is recognizable, there is evident, connecting 

 it with the primary vascular strand, a short group of procambium cells, and the 

 stem apex is seen to occupy the space between these two leaf traces. No procambium 

 is developed in the stem above the junction of the leaf traces, but the inner cells, derived 

 from the apical meristem, contribute solely to the medullary tissue of the sporophyte 

 (fig. 121, A). 



Fig. I2i. Dantea jamaicensss. 



A. Large embryo, cot, cotyledon; / 2 , second leaf. X 50. 



B. Median section of cotyledon; h, epidermal scale. X95. 



C. Second leaf. X150. 



D. Trichomcs from apical region. 



The first tracheary tissue arises in the mid-region of the young sporophyte and 

 consists of a group of short reticulate tracheids. From this point the development 

 of the tracheary tissue proceeds upward into the cotyledon and downward into the 

 root. The single strand of tracheary tissue in the cotyledon is seen to be continuous 

 with one of the xylem masses of the diarch root. The second xylem of the root arises 

 somewhat later and is connected with the xylem of the second leaf. This second 

 xylem mass is decidedly smaller than the first one, at least in Danaa, where I have 

 studied this point carefully, and an examination of the other genera points to a 

 similar inequality in the xvlems of these as well, but this may not always be the case. 



1 in. COTYLEDON. 



The cotyledon at a very early period bends strongly over the stem apex, very 

 much as it does in Botrychium virginianum, and very soon afterwards begins to 

 flatten out, so as to indicate the separation of the lamina from the petiole. The 

 flattening of the apex is followed, in many cases at least, by a true dichotomy, which 

 is soon repeated, so that the lamina becomes fan-shaped, with a strictly dichotomous 

 venation (fig. 87, G, H; fig. 127). This shows especially well in Marattia iouglasti. 

 In M. sambuctna (fig. 87, C) the cotyledon is more nearly orbicular than in M. 

 douglasti, but the venation indicates a similar early dichotomy of the apex. 



In Angiopteris, the form of the cotyledon is extremely variable (fi^. 124). 

 Farmer states that it has a distinct midrib extending to the apex of the cotyledon 



