244 



THIRD GROUP. VASCULAR CRYPTOGAMS. 



longitudinal rows as small closed pouches, which are now some distance from one 

 another, though they were closely packed together inside the capsule. These pro- 

 ceedings occupy a few hours, till at length the spores of both kinds are set free, and 

 with a suitable temperature fertilisation is accomplished in from twelve to eighteen 

 hours after the sporocarp is placed in water. 



a. Histology. The formation of the tissues in the heterosporous Ferns agrees in 

 the most important morphological points with that of the homosporous (vid. supra). 



The epidermis shows some peculiarities, especially 

 in the matter of the stomata ; the fundamental tissue 

 has the large intercellular spaces that are common 

 in water and bog plants ; the formation of scleren- 

 chyma in the leaves and in the walls of the capsule 

 in the Marsiliaceae is described by Braun and 

 Russow. The vascular bundles especially in the 

 Marsiliaceae are very similar in composition to 

 those of the true Ferns ; there is a central xylem 

 surrounded by phloem, and round the phloem is 

 a bundle-sheath of a single layer of cells with wavy 

 lateral walls. A single bundle traverses each root 

 and leaf-petiole ; this bundle divides in the lamina 

 of the leaf in Marsilia and produces a dichotomous 

 venation ; the vascular bundles in the stem of the 

 Marsiliaceae, as seen in transverse section, form 

 a cylinder filled in with fundamental tissue 1 . 



b. Classification. The account already given in 

 the text has made it plain, that the heterosporous 

 Ferns fall naturally into two very distinct families : 

 the Salviniaceae, which are closely allied to the 

 homosporous Ferns, and the Marsiliaceae, which 

 have not much in common with the homosporous 

 Ferns, with similar formation of sporangia ; but 

 the insertion of the sporocarp on the sterile portion 

 of the leaf recalls a similar relation of the sporo- 

 phyll to the sterile portion of the leaf in the 

 Ophioglosseae. 



Family i. SALVINIACEAE. Plant floating hori- 

 zontally on the water ; stem with an apical cell 

 forming two rows of segments, right and left ; sori 

 male or female, one in each unilocular sporocarp ; 

 spores invested by frothy hardened mucilage (mas- 

 sulae, episporia) ; the microspores in Salvinia 

 form a prothallium, which though very simple 



emerges from the spore ; the prothallium of the macrospore is a vigorous growth, and 

 bears several archegonia ; Salvinia is rootless, Azolla has roots. 



Family 2. MARSILIACEAE. Plant creeping on wet ground or sometimes floating ; 

 stem with a three-sided apical cell, which forms two latero-dorsal rows of segments, 

 and one ventral ; each sorus comprises macrospores and microspores, and two to 

 many sori are enclosed in a plurilocular sporocarp. Spores invested by hardened 

 mucilage forming episporia which show radial prismatic structure, and have to 

 some extent the power of swelling. Microspores and macrospores remain for a long 



FIG. 200. Marsilia. sal-vatrix. A a sporocarp 

 in natural size ; si the upper part of its stalk. /? a 

 sporocarp which has burst in water and allowed 

 the gelatinous ring- to protrude. In C the gelatinous 

 ring. is ruptured and stretched out ; sr the compart- 

 ments of the sorus, sch shell of the sporocarp. D 

 a compartment of an unripe sporocarp with its 

 sorus. E a similar one from a ripe sporocarp; mi 

 microsporangium, ma macrosporangium. B after 

 Hanstein. 



1 See above on the histology of the homosporous Ferns. 



