F1L ICINEAE. HETER OSPOR US FI LI CINE A E. 



233 



Thus the oospore l divides by basal, transversal and median walls into octants, one of 

 which on the side turned towards the prothallium produces the young stem, one 

 turned towards the neck of the archegonium the young root (wanting in Salvinia 

 which has no roots), two produce the foot and two the cotyledon. There is a second 

 cotyledon in Marsilia formed from the fourth octant of the epibasal half of the 

 embryo which is not employed in the homosporous Ferns to form the organs. 

 Azolla too according to Berggren has a second cotyledon, which also proceeds 

 from the fourth octant of the epibasal half, while one of the other three produces 

 the stem and the two others the cotyledon, which in the Salviniaceae is often termed 

 the scutiform leaf. 



The subsequent growth of the genera in this group, though they differ much in 

 general habit, has one point which is the same in all, namely that it is distinctly 



FIG. 186. Marsilia Salvatrix. A the prothallium // projecting from the ruptured coat r of the spore, si layers of 

 mucilage forming the funnel with numerous spermatozoids. B vertical section of a prothallium// with the archegonium 

 a and the oosphere o. C, D, E young embryos ; J apex of the stem, * cotyledon, w root, f foot. B E after Hanstein. 



dorsiventral. As in the homosporous so in the heterosporous Filicineae a leaf 

 is not produced from every segment of the apex of the stem, as is the case in the 

 Muscineae and Equisetaceae, but certain segments remain sterile and are employed 

 in forming the internodes. The growth of the leaves is basifugal, as in the homo- 

 sporous Ferns and Ophioglosseae, and by means of an apical cell which gives off 

 alternating segments in two rows. Before the development enters on an unvarying 

 course, the young plant shows an increase of strength both in the greater size of the 

 leaves and the greater perfection of their form and in a change in their relative 

 positions ; but to make this clear, it will be necessary to give a separate consideration 



The macrospores float in water in such a manner that their longitudinal axis is nearly 

 horizontal. Since the basal wall nearly coincides with the axis of the archegonium, it is also 

 nearly horizontal and divides the embryo into an upper or epibasal half which gives rise to the stem 

 and one or two cotyledons, and a lower half which produces the foot and root. Fig. 187 therefore 

 does not show the true position of the macrospore, which must be supposed to lie horizontally to 

 the left, so that the roots and root-hairs (wk} of the prothallium are directed downwards. 



