240 



THIRD GROUP. — VASCULAR CRYPTOGAMS. 



apex, and there forms three or three times three large masses of the same substance, 

 and runs out besides into a tuft of delicate threads; in these forms the mucilage, 

 which contains air in its pores, serves as a floating apparatus for the macrospore, 

 which by its means carries also with it the upper part of the ruptured sporangium. 



The sporocarps of the Marsiliaceae are of much more complicated and firmer 

 structure than those of the preceding family. Those of Pilularia are roundish 

 capsules with a short stalk, and their morphology is still obscure. The capsule, 



which is surrounded by a thick and hard 

 wall composed of several layers of cells 

 and filled with soft succulent parenchyma, 

 contains hollow chambers reaching from 

 the stalk to the apex ; P. globulifera has 

 four of these chambers (Fig. 195), P. minuta 

 two, P. americana three. Each chamber 

 has on the side towards the wall of the 

 capsule a cushion-like placenta, which as- 

 cends from below through the length of the 

 chamber and has a vascular bundle behind 

 it ; on this placenta are placed the stalked 

 sporangia, forming a sorus which has macro- 

 sporangia chiefly at its lower end and 

 only microsporangia above. It is probable 

 that each chamber has in its young state 

 an open passage at its apex^; how far 

 the delicate tissue which surrounds the 

 sorus inside the chamber can be compared to an indusium, as is done by many 

 botanists, is uncertain both in this case and in Marsilia. Juranyi has recently 

 published a contribution to the history of the development of the sporocarp of 

 Pilularia ^ From this it would appear probable, as the analogy of Marsilia would 

 itself suggest, that the sporocarp is a metamorphosed segment of the leaf, by the side 

 of which the sporocarp when mature appears to stand. The sporophyll then would 

 occupy the same position in regard to the sterile segment of the leaf in Pilularia as in 

 the Ophioglosseae. The sporocarp, is at first a small body composed of cellular 

 tissue, with one vascular bundle. It next becomes club-shaped and concave on the 

 side towards the sterile leaf. Four leaf-lobes then appear in it, from which the main 

 body of the sporocarp proceeds and which form the valves of the sporocarp. The 

 sporangia are formed in cavities, the edges of the leaf-lobes unite, and the sporocarp 

 becomes pear-shaped. The four rows of cells visible in the figure would then be the 

 lines of union of the four leaf-lobes. 



The sporocarps of the various species of Marsilia are usually somewhat bean- 

 shaped capsules with very hard waUs and with stalks of varying length. They are 



FiCi. 195. Transverse section of tiie sporocarp of 

 Pilularia globuli/era below the middle, where the macro- 

 sporangia and microsporangia are mingled together ma and 

 mi\ g the vascular bundles, /; hairs, ^ the epidermis of the 



* This is really the case according to my observations ; the sori therefore are not formed inside 

 closed cavities, as has hitherto been assumed. 



^ Juranyi, Ueber d. Gestaltung d. Frucht bei Pilularia globulifera (Report in Bot. Centralblatt, 

 1880, p. 201). The account in the text is an imperfect one, and further investigation is desirable. 



