]^20 THE MARATTIALES 



equal parts (fig. 87, J). A rhizoid may be cut off either before or after this first 

 transverse wall is developed, but frequently no rhizoids are formed until a much 

 later period, as in Ophioglossum. The primary rhizoid, when present, is formed 

 much as in the typical ferns, the papilla from which it develops being cut off from 

 the larger cell, and it contains little or no chlorophyll. Each of the primary prothal- 

 lial cells divides, in typical cases, by a longitudinal wall, so that the young gameto- 

 phyte consists of four cells, arising quadrant-wise (fig. 88, A), and closely resenibling 

 corresponding stages in Ophioglossum, except for the absence of chlorophyll in the 

 latter. Where the young plants are crowded or light is deficient, as for instance 

 when the germination occurs within the sporangium, there is a tendency to the 

 development of a filament, a phenomenon often met with also in the typical ferns. 

 Usually one of the upper pair of cells in the four-celled stage assumes the role 

 of an apical cell, and for some time, as in the typical ferns, there is growth from a 

 two-sided apical cell (fig. 88, C). As soon as the apical cell is established, it grows 



Fig. 87. 



A. Two germinating spores of Marattia jraxinea Smith. X200. The remains of the spore membrane can be se^n. 



B. Young gametophyte of same species. X75. (A, B, after Jonkmann). 



C. Marattia samhucina Blume. X 1.5. 



D-H. M. douglasii Baker. D-F, X 1.5; G, H, X3. G, H, show the young sporophyte. 



D and E represent the same prothaUium after an interval of about a year. F is the ventral view of E . k, adventitious bud . 



very much as it does in such a liverwort as Aneura and produces a thallus of the 

 same form and structure. But as the prothaUium grows older a periclinal wall 

 is formed in the apical cell, and in the outermost of the two cells thus produced 

 there is a longitudinal wall dividing it into two equal cells, and from this time on 

 it is impossible to recognize a single apical cell in the prothaUium, the apex of which 

 is occupied by a group of apparently similar marginal initial cells. 



At first the prothaUium has a spatulate form, but before the single apical cell 

 is replaced by the group of marginal initials the outer cells of the younger segments 

 grow more rapidly than the inner ones, so that they project beyond the apical cell, 

 which thus comes to lie in a depression between the two lobes, and the familiar 

 heart-shaped form so commonly found in the prothaUium of most ferns is estabhshed. 

 The marginal initial ceUs vary in number with the width of the depression in which 

 they lie. In a horizontal section they appear oblong in form, but in the vertical 

 sections made they have a semicircular outline (fig. 88, D, E). 



