408 M. Schleiden on the Fructification of the Rhizocarpese. 



XLV. — On the Fructification of the RhizocarpeEe. 

 By M. J. Schleiden *. 



For the development of a new individual in Rhizocarpea, two very 

 distinct parts separate from the old plant, namely pollen grains 

 and ovules. The former have the usual structure, consisting of 

 a cell (the pollen-cell) and the outer pollen membrane. The 

 ovules exhibit the following structure : a very large, firm-walled 

 cell, containing very large starch granules, mucilage and oil (the 

 embryo-sac), is inclosed in a white coriaceous membrane, which 

 is formed of cells so very small as to be almost indistinguishable ; 

 this membrane forms a papilla (the nucleus) at one end, which 

 is sometimes clothed either by three lobes of the same membrane 

 as in Salvinia, or by an envelope composed of these three lobes 

 united together so as to leave an orifice at the apex as in Marsilea ; 

 this is called the simple coat of the ovule (integumentum simplex) . 

 The whole is inclosed in a cellular sac (sacculus) as in Salvinia, 

 or surrounded by a layer of quite gelatinous and almost confluent 

 cells, as in Pilularia and Marsilea. The cell of the pollen grain 

 extends itself into a longer (Salvinia) or shorter (Pilularia) tube. 

 Simultaneously the cells of the nucleus develope toward the apex 

 of the embryo-sac, become clearly distinguishable and more lax, 

 filled with chlorophylle, &c, and break through the nucleus so that 

 they project free {mammilla nuclei) . If a pollen tube now comes in 

 contact with these cells it penetrates deeply between them and 

 reaches a layer of smaller green cells, immediately clothing the 

 embryo-sac (Pilularia and Salvinia), and then expands as a ve- 

 sicle ; it thus displaces the surrounding cellular tissue, which how- 

 ever continues to develope and protrudes from the ovule as a 

 larger or smaller green body ; in Salvinia it elongates into two 

 lateral, connected processes, while in Pilularia a portion of the 

 cells of the upper surface extend themselves into long, hair-like 

 fibres. In the utricular end of the pollen tube cellular tissue is 

 developed, which, becoming the embryo, finally breaks through, 

 with one end, the mammilla nuclei of the ovule, which now exhibits 

 the appearance of a thin-walled sac ; the latter on the occurrence 

 of this process assumes the form of a round sheath (Pilularia), 

 or a flat, bilabiate body (Salvinia) . In Salvinia the protruding 

 embryo forms a stem which spreads out above into a flat disc, 

 floating on the water (primary leaf, cotyledon) ; from its point of 

 attachment, at the lower part of a vertical fissure in it, a bud 

 already somewhat developed produces into a little stem, bearing 

 leaves on both sides and sending out radicles below. In Pilu- 



* Translated by Arthur Henfrey, F.L.S., from Schleiden's ' Grundzuge 

 der Wiss. Botanik,' 2 Th.'p. 100. 



