RHIZOCARPEM. 



3«7 



covered with four superficial cells arranged in 

 latter a wall arises inclined from without inw 

 another similar partition (Fig. 288 /, a, b, c). 

 By the succeeding growth these cells are 

 transformed into four rows each consisting 

 of three segments lying one above another 

 (//, ///), the lower of which are termed 

 * closing cells,' the upper pair the neck {III, 

 h). In the meantime a new cell arises at the 

 apex of the central cell, which, with its coni- 

 cal point, forces itself between the closing 

 cells (/, d, III, d), and forms the canal-cell, 

 first discovered by Pringsheim. It becomes 

 transformed into mucilage, which escapes 

 from the canal laid open by the throwing oft' 

 of the neck. The whole contents of the cen- 

 tral cell (/, //, ///, e) becomes the oosphere. 

 After fertilisation has been accomplished, the 

 canal again closes by the lateral approximation 

 The prothallium of Marsilea and Pilularia 

 of tissue from the apical papilla of the ma- 

 crospore, after it has ruptured the cell-walls 

 of the spore at that place (Fig. 290, A, B), 

 and remains buried at the bottom of the 

 funnel formed from the outer membranes of 

 the macrospore. Even at an early period, 

 before the rupture, Hanstein asserts that the 

 large central cell may be recognized in it, 

 surrounded, in its entire circumference, at 

 least at first, by a single layer of cells, so 

 that the prothallium bears originally in this 

 case only a single archegonium. The central 

 cell is here also covered by four cells ar- 

 ranged as a cross, which form at the same 

 time the apex of the whole prothallium. By 

 a similar process to that which occurs in 

 Salvinia, they form the free neck-pordon 

 (which in Marsilea projects only slightly, in 

 Pilularia very much) and the closing cells of 

 the archegonium. Above the central cell, 

 the protoplasm of which contracts, a small 

 canal-cell is visible, according to Hanstein, 

 penetrating between the closing cells, and 

 behaving as in Salvinia. Even Hanstein was 

 unable to recognize any further cell-forma- 

 tion w^ithin the central cell ; the whole of 



c c 2 



the form of a cross ; in each of these 

 ards, followed in each inner cell by 



Pig. 288.— Development of the archegonia of 

 Salvhiia nataiis (after Pringsheim, X150). 



of the closing cells. 



is developed as a hemispherical mass 



Fig. -z^g.— Salvinia natans ; median longitudina 

 section through the prothallium and young embryo ; 

 A after the first three divisions of the oospore, / the 

 first segment divided by the wall ji/ into the cells a and 

 b; 11 the second segment, cut ofl" by the wall 2 from 

 the apical cell v; cd axis of growth ; B embryo in a 

 further stage of development, rrr first stage of the 

 foot, s apical cell of the scutiform leaf. III— VI the 

 succeeding segments, v apical cell of the stem, m in 

 A and B the closing cells of the archegonium (after 

 Pringsheim). 



