206 THIRD GROUP. VASCULAR CRYPTOGAMS. 



in the epibasal and hypobasal halves with the same direction as the basal, the 

 epibasal (Fig. 153 e), and the hypobasal wall (Fig. 153 h\ These walls show in all 

 side views of the embryo as anticlinal walls, in the front and hinder views as periclinal 

 walls. It is the same in Fig. 153 A where the basal wall is in the plane of the 

 paper. The portions separated off by the epibasal and hypobasal walls on both 

 sides of the basal wall are called by more recent writers the epibasal and hypobasal 

 segments ; concerning their further divisions we will only say here, that by two 

 anticlinal walls having the same direction as the transversal wall, which are then 

 connected by periclinal walls with the transversal wall, an inner mass of cells which 

 in transverse section has nearly a quadratic form is divided off from an outer tissue 

 which forms the cortex. 



The epibasal half of the embryo after the appearance of the epibasal wall 

 consists of the epibasal segment and four anterior cells which have the form of three- 

 sided apical cells. One of these cells is in fact the apical cell of the stem, and walls 

 are formed in it which are parallel to the basal, transversal and median walls in turn. 

 Thus a persistent apical cell is produced, which is in form a three-sided pyramid. 

 The cotyledon which proceeds from two octants on the other hand shows no such 

 apical cell ; the leaves which are formed later will be noticed further on. 



The cotyledon and the primary root remain small ; the latter dwindles away very 

 early in the Hymenophylleae, and in many species of the group no fresh roots are 

 formed, and their place is taken by subterranean shoots. When the cotyledon and 

 the root have reached a certain size, they break through the venter of the arche- 

 gonium, the root penetrates into the ground, and the cotyledon and the young stem 

 bend upwards. New leaves then arise on the latter. The later-formed leaves are 

 always larger, their form more complicated, and the structure of the stem, as the 

 parts added by longitudinal growth increase in thickness, becomes continually more 

 highly developed: the first portions of the stem like the primary leaf-stalks have only one 

 axile vascular bundle each, the later portions have several, as soon as stem and leaf 

 have attained some size. Thus the Fern goes on increasing in strength, not by sub- 

 sequent enlargement of the parts of the embryo, but by each succeeding part 

 attaining a greater size and higher development than the preceding, till at length a 

 kind of stationary condition is reached, in which the new organs that are formed are 

 about equal to the preceding ones. The following remarks refer especially to this the 

 fully-developed condition of our plants ; but before we proceed to them, we must 

 first mention the peculiar phenomenon which De Bary 1 has minutely investigated, 

 and to which he has given the name of apogamy or loss of sexual propagation. 

 There are, that is to say, Ferns in which the sexual generation, the prothallium, 

 produces the asexual generation, the fern-plant, not by the development of an 

 oosphere fertilised in the archegonium, but by the formation of a shoot. This 

 phenomenon is at present known only in Pteris cretica*, Aspidium Filix-mas var. 

 cristatum, Aspidium falcatum, and Todea africana 3 . In Pteris cretica the prothallium 



1 Ueber apogame Fame u. d. Erscheinung d. Apogamie im Allgemeinen (Bot. Zeit. 1878, 

 p. 449). [Leitgeb, Die Sprossbild. an apogam. Farnprothallien (Ber. Deutsch. Bot. Ges. Ill, 1885.] 



2 Described for the first time in this species by Farlow in Bot. Zeit. 1874, No. 12, [and in 

 Q. J. M. S. 1874]. 



8 On Todea see Sadebeck, loc. cit. p. 231. 



