THIRD GROUP. VASCULAR CRYPTOGAMS. 



same leaf; the plant is therefore monoecious. The microsporangia in a sporocarp 

 are many in Azolla and in Salvinia ; several macrosporangia are formed within one 

 indusium in Salvim'a, one only in Azolla. All the spores formed from the sixteen 



mother-cells in a microsporangium come to maturity, 

 whereas only one of the four times sixteen spores 

 developes in a macrosporangium, so that in 'Azolla, 

 where as was said there is only one macrosporangium 

 in a sporocarp, there is but one macrospore inclosed 

 before maturity in the indusium, and within this by the 

 wall of the sporangium which perhaps eventually 

 disappears. 



The sporangia are capsules with long stalks and 

 a wall which in the mature state is formed of one 

 layer of cells ; the macrosporangia have short stalks. 

 The formation of the sporangia has been observed 

 by Juranyi. The placenta has an upper layer of cells 

 which are elongated in the radial direction ; each of 

 these cells grows out into a papilla and thus forms 

 the rudiment of a sporangium ; the papilla divides 

 by a transverse wall into a lower and an upper cell ; 

 the lower cell produces by repeated transverse di- 

 visions the long segmented stalk, which in the 

 macrosporangia (not in the microsporangia) consists 

 eventually through longitudinal divisions of several 

 rows of cells. The upper cell after a time swells 

 into a hemispherical form, and produces the body of 

 the sporangium by cell-divisions exactly similar to those 

 which take place in the Polypodiaceae (Fig. 165); in 

 this way a wall of one layer of cells is formed, and inside it is the tetrahedral arche- 

 sporium surrounded by a layer of cells densely filled with protoplasm; the archesporium 

 by repeated bipartitions produces the sixteen mother-cells of the spores (sporocytes), and 

 the surrounding layer developes into two layers of tapetal cells. The sixteen spore- 

 mother-cells divide each of them into four young spore-cells tetrahedrally disposed. 

 Up to this point the processes are the same in the microsporangia and in the macro- 

 sporangia. All the four times sixteen spores develope in the microsporangia ; they 

 separate from one another and lie without any particular arrangement inside the 

 sporangium, while the tapetal cells become disorganised and changed into a frothy 

 mucilage which subsequently hardens and encloses the spores *. But in the macro- 

 sporangia only one of the newly formed four times sixteen spores developes ; this one 

 however increases so greatly in size, as at length almost to fill the cavity of the 

 sporangium, and at the end which is towards the apex of the sporangium there is a 

 large nucleus. During the growth of the macrospore the tapetal cells, and at a later 

 period all the undeveloped spores also, become disorganised and run together into a 

 frothy plasm, which spreads over the wall of the macrospore and forms a specially 



FIG. 193. Longitudinal section of a root 

 of Marsflza Salvatrix ; lus apical cell, Tuh\, luhl 

 the first, iv/i3, ivh* the second, wka the third 

 root cap, each cap consisting of two layers, xy 

 the youngest segments of the root, o the epi- 

 dermis, gf vascular bundle, /; the parts of the 

 root-cap which extend farthest back. 



1 See the remarks in the Introduction. 



