356 Dr. L. Radlkofer on Fecundation in the Vegetable Kingdom, 



cells originally covering the central cell, but also those lying 

 beside them, undergo repeated division by ci'oss-septa, parallel 

 to the outer surface of the prothallium, -uhere the neck of the 

 archegonium appears immersed in the substance of the prothal- 

 lium instead of projecting in a cylindrical form above it. 



In Salvinia, finally, this neck of the archegonium is composed 

 exclusively of these four covering-cells. The archegonial canal 

 leading to the central cell is then a short intercellular passage 

 formed by the separation of these cells at their common com- 

 missure. Two germinal vesicles are often formed in the central 

 cell here'^^. 



The transformation of the germinal vesicle into the embryo, 

 and its subsequent development, follow essentially the same type 

 as in the Equisetacese and the Ferns. 



The statements of earlier observers, that when the microspores 

 and megaspores are kept apart, the latter produce prothallia, 

 but no young plants, are confirmed by Hofmeistcrf. 



The microspores are formed inside spore-cases comparable with 

 those of the Ferns, collectively enclosed, with the megaspores, 

 in a common envelope, which constitutes the fruit [receptaculum) 

 of the Rhizocarpere. Their development is according to the same 

 type as that of the formation of pollen in the Phanerogamia, in 

 special mother-cells arranged tetrahedrally inside a mother-cell. 

 The megaspjore is produced by the preponderating growth of 

 a young spore of this kind, accompanied by the displacement of 

 not merely the other young spores contained in the same mother- 

 cell, but also of all the rest of the spores in the whole sporange 

 (together with their enveloping mother-cells). In Salvinia, the 

 microspores and megaspores are contained in separate receptacles. 



The analogy of structure between the large spore of Azolla 

 and that of Salvinia, as also between the microspores of the 

 same genera, has been demonstrated by jMetteniusJ. 



Lycopodiace.e. — A. Selaginellete. — The excellent researches 

 of Mettenius§ and Hofmeistery show us that the small and large 

 spores of the Selaginellea behave exactly like the microspores and 

 megaspores of the preceding groups, both in reference to their 

 mode of development and their import in the])rocess of reproduction. 



As regards the first, it will suffice to observe, that the course 

 of development of the meg aspore- capsule [Kugel-kapsel, Hofm.) 

 is the same as that of the microspore-capsule [Staub-kapsel, Hofm.), 



* Flora, 1854, p. 257. 



"t" Among them was P. Savi, Sulla Salvinia natans, &c. Biblioth. Italic. 

 XX. (G. L. Duvernoy, De Salvinia nat. Dissert. Tubingen, 1825, p. 5). 

 J Linnffia, xx. (1847) ; Ann. des So. nat. 3 ser. ix. p. 116 (1848), 

 § Beitr. z. Botanik, p. 7. 

 II Vergleich. Untersuch. p. 118. 



