232 



THIRD GROUP. — VASCULAR CRYPTOGAMS. 



formed by the side of the first and right and left of it, so that they form a transverse 

 row parallel to the anterior side or apical line. If the oosphere in one of these 

 archegonia is fertilised the work of the prothallium is accomplished ; otherwise the 

 prothallium continues to grow on its anterior side and produces from one to three 

 fresh transverse rows of archegonia, and each row may contain from three to seven 

 archegonia. The elongated oosphere in each archegonium lies obliquely in the 

 tissue of the prothallium with its outer, that is the neck-end, looking backwards, 

 and the inner and deeper end towards the anterior extremity of the prothallium ; 

 it is in the latter position that the apical cell of the young stem is subsequently 

 found. The development of the archegonium is exactly the same as in the homo- 

 sporous Ferns ; Pringsheim was the first who observed the canal-cell of the neck. 

 The prothallium oi Azolla'^, the second genus of the Salviniaceae, has usually but 

 one archegonium, and only produces more when the first is not fertilised. 



The prothallium in Marsilia and Pilularia emerges as a hemispherical mass of 

 tissue from the apical papilla of the macrospore after rupture of the membranes of 

 the spore at that spot (Fig. 186, A, B), and lies 

 concealed at the bottom of the funnel formed by the 

 outer membranes of the macrospore. The central 

 cell of the archegonium, enclosed in the prothaUium 

 which consists of one layer of cells only (Fig. 186), 

 is here also covered by four cells placed crosswise, 

 which at the same time form the apex of the whole 

 prothallium ; they produce the neck of the arche- 

 gonium, which in Marsilia projects only a little, in 

 Pilularia considerably, by much the same process 

 as in Salvinia ; here too according to Hanstein a 

 small neck-canal-cell, which pushes itself in between 

 the lid-cells and which behaves as in Salvinia, may 

 be distinguished above the central cell, the proto- 

 plasm of which contracts. The ventral canal-cell 

 is cut off as a very small portion of protoplasm 

 from the large protoplasmic body of the central 

 cell, which rounds itself off into the oosphere. 

 After fertilisation the layer of tissue surrounding 

 the central cell is doubled, a few chlorophyll- 

 granules are formed in it, and its outer cells 

 develope in Marsilia Salvatrix (Fig. 187) into long rhizoids which grow more 

 luxuriantly if no fertilisation takes place. In Marsilia Salvatrix the spermatozoids 

 gather in great numbers in the funnel above the prothallium at the time of 

 impregnation, and force their way into the neck of the archegonium. 



Development of the second, asexual getieratiojt {sporophore, sporophyte). The order 

 of formation of the cells and the mode of development of the organs in the embryo 

 agree exactly with the same processes already described in the homosporous Ferns. 



Fig. 185. Development of the archegonia of 

 Salvinia natans. a, b, c the divisions in the 

 neck-cells, d the neck-canal-cell, e oosphere from 

 which the ventral canal-cell, not shown in the 

 figure, is subsequently cut off, /i neck-cells. As the 

 divisions of the neck-cells by the walls a, b, c are 

 fonned when the neck is only just protruded 

 above the prothallium, these walls appear to be 

 inclined. In the Ferns the divisions of the neck- 

 cells are not formed till after the protrusion of 

 the neck. After Pringsheim. Magn. 150 times. 



jren, Om Azollas prothallium och embryo (Lunds Univ.-Arsskrift, T. XVI, reported in 

 Bot. Zeit. t88£, p. 565;. 



