44^ VASCULAR CRYPTOGAMS. 



undergoing still further division. The four hypobasal octants give rise to the foot. 

 Thus no root is developed at this period, nor is one developed subsequently; 

 Salvinia is absolutely roodess. In order to understand the subsequent processes 

 of growth, Fig. 311 must be compared with Fig. 313. The growing embryo 

 bursts the prothallium; from r r r, in Fig. 313 Z?, arises the foot (caulicle) of 

 the young plant (Fig. 311 a)\ from s, Fig. 313 B^ is formed the scutiform leaf 

 (Fig. 3ii.j5, /^), by the growth of which the terminal bud of the stem becomes 

 directed downwards (Fig. 311 A, v). The epibasal part of the embryo faces the 

 anterior side, its hypobasal part the posterior side of the prothallium ; its axis of 

 growth lies in the same plane with the median line of the latter. 



The first divisions of the embryo of Marsilia Salvatrix agree in all essential 

 points, according to Hanstein's observations and my own, with those of Salvinia; and 

 Hanstein states that this is also the case with Pilularia; but in both these genera the 

 rudiment of the first root is visible at an early period. The stem in these genera 

 also creeps or floats in a horizontal direction from the first, as in Salvinia, and 

 forms a number of roots in acropetal succession. Fig. 314 shows the first divisions 

 of the embryo of Marsilia Salvatrix. The oospore is divided by a nearly vertical 

 basal wall into an anterior (epibasal) larger and a posterior (hypobasal) smaller 

 cell : these are divided, as in Salvinia and in Ferns, by a transverse and by a 

 median wall, so that the embryo consists of eight cells. Of the four epibasal 

 octants, one of the two upper ones becomes the apical cell of the stem, whilst 

 the other gives rise to the second leaf (cotyledon) ; from the lower two the first 

 leaf (cotyledon) is developed. Of the four hypobasal octants, the lower one, which 

 is diametrically opposite to the apical cell of the stem, gives rise to the primary 

 root, the other octant at the same level becoming suppressed : the two upper 

 ones give rise to the foot (Fig. 314 -£', /"). The union between embryo and 

 prothallium is brought about by the foot. The apical cell of the stem, Fig. 314 

 E, s, thus lies, after the formation of the first three walls, between the anterior 

 margins of the first leaf and of the foot. In the stage represented in Fig. 315 

 this origin of the first leaf, first root, and foot, may still be recognised from the 

 arrangement of the cells. 



The further growth of the three genera, otherwise very different in their habit, 

 to which we must add Azolla, although its development has not yet been investigated, 

 agrees in maintaining the bilateral structure already manifested in the embryo in 

 connection with the decidedly horizontal growth, although, as we shall see, the 

 position of the apical cell and of its segments varies. In contrast with Muscineae 

 and Equisetaceae, but in accordance with Ferns, a leaf is not produced in the Rhizo- 

 carpeae from every segment of the stem ; certain of the segments remain sterile, and 

 these then go to the formation of internodes. The leaves grow, as in Ferns and 

 Ophioglossaceae, basifugally by means of an apical cell which forms two rows of 

 alternating segments. Before the development has assumed a constant course, an 

 increase of vigour of the young plant takes place, which is shown in the enlarge- 

 ment of the leaves and the greater perfection of their forms, as well as in a change 

 of their relative positions. But in order to make this clear, it is necessary to 

 observe separately Salvinia on the one hand, and the Marsiliaceae {Marsilia and 

 Pilularia) on the other. 



