454 VASCULAR CRYPTOGAMS. 



sporocarp and by that of the sporangium (which subsequently disappears ?). The 

 sporangia are capsules borne on long stalks, the wall of which, when mature, 

 consists of a single layer of cells. The macrosporangium is shortly stalked and 

 probably arises from the apex of the columella. 



The development of the sporangia in Salvinia has recently been investigated 

 by Juranyi. The columella is covered with a layer of radially elongated cells, each 

 of which grows out into a papilla and forms the rudiment of a sporangium. The 

 papilla is divided by a transverse septum into a lower andean upper cell. The lower 

 one undergoes repeated transverse divisions and forms the long, segmented stalk, 

 which comes to consist of several rows of cells by means of longitudinal divisions in 

 the case of the macrosporangia only; the upper one assumes a hemispherical form and 

 gives rise to the body of the sporangium by means of divisions which are similar to 

 those occurring in the Polypodiaceae (see Fig. 305). A wall is formed consisting 

 of a single layer of cells, within which is a single tetrahedral cell, the archesporium. 

 From this, four flat segments are cut off which form a layer of cells containing 

 much protoplasm surrounding the tetrahedral central cell. The central cell, by 

 repeated division, gives rise to the sixteen mother-cells of the spores, and meanwhile 

 the layer investing it has undergone division into two layers which together form the 

 tapetum. Each of the sixteen mother-cells of the spores then divides into four 

 tetrahedrally placed spore-cells. Up to this point the processes are the same in 

 both micro- and macrosporangia. In the microsporangia all the sixty-four cells 

 develope ; they become separate and are scattered irregularly in the cavity of the 

 sporangium. The tapetum becomes disorganised and forms a frothy mucilage, 

 which subsequently hardens, in which the spores are enclosed. In the macro- 

 sporangia only one of the sixty-four rudimentary spores continues to develope ; 

 it becomes enormously enlarged so that finally it nearly fills the cavity of the 

 sporangium. A large nucleus lies at that end of the macrospore which is directed 

 towards the apex of the sporangium. During the growth of the macrospore the 

 tapetum, and subsequently all the other undeveloped spores, undergo disorganisation, 

 becoming converted into a frothy plasma which is in contact with the outer coat of 

 the macrospore, and is especially accumulated at its apex. It is this frothy plasma 

 which becomes hardened and forms a thick investment for the mature macrospore, 

 termed the Epispore (Fig. 311, A), which splits even during its formation into three 

 lobes over the apex of the spore, so as to permit of the subsequent outgrowth 

 of the prothallium. 



Strasburger had already demonstrated the existence of this hardened frothy 

 mucilage in both kinds of sporangia of Azolla, but in this plant it assumes a far 

 more conspicuous appearance. In the microsporangia the mucilage looks like a 

 large-celled tissue, and forms from two to eight separate clumps [Massulce), each of 

 which encloses a number of microspores. In some species [A. filiculoides, Caro- 

 liniand) these massulae have their surfaces covered with hair-like appendages, 

 barbed at their free ends {Glochidia), by means of which they attach themselves, 

 when they have escaped from the sporangia, to the floating macrospores. The 

 macrosporangium of Azolla contains a single spheroidal macrospore, which does not 

 nearly fill its cavity, the whole surface of which is completely covered with a thick rugose 

 layer of this hardened frothy mucilage. It projects from the apex of the spore and runs 



