SPECIAL MORPHOLOGY : RHIZOCARPE^. 203 



all events, in the parts of the flower. In the Phanerogamia the 

 anther is unquestionably only a modified leaf, the seed-bud (ovule) 

 probably only the modified extremity of a stem ; in the Rhizo- 

 carpece no explanation of the kind can be given, from the imperfect 

 knowledge of the course of development. 



a. Plantce athalamicce. 



115. The character of this group, and the distinction from 

 the Phanerogamia^ is the fact that the seed-bud (ovule) and pollen 

 separate as independent bodies from the plant, and the tubular ex- 

 pansion of the pollen-cell penetrates the seed-bud subsequently, 

 and then becomes developed into a perfect plant in one act of 

 vegetation. 



IX. RHIZOCARPE^E. 



116. In the Rltizocarpea two very distinct parts become 

 detached from the old, in order to the production of a new 

 individual, namely, pollen-grains and seed-buds (ovules). The 

 former have the usual structure, consisting of a single cell (pollen- 

 cell), with an external pollen-membrane. The others present the 

 following structure : a very large cell, with firm walls, containing 

 large grains of starch, mucilage, and oil (the embryo-sac], is sur- 

 rounded by a white, coriaceous membrane, which is formed of very 

 minute, scarcely distinguishable cells ; this membrane forms, at one 

 extremity, a papilla (nucleus), which is covered sometimes by three 

 lobes of the same membrane (in Salvinia), or by these three united 

 into an envelope open at the point (in Marsilea), which is called 

 the simple coat of the bud (integumentum simplex). The whole is 

 enclosed in a cellular sac, the sac of the seed (sacculus) (as in 

 Salvinia), or in a layer of cells so gelatinous as to be almost con- 

 fluent (as in Pilularia and Marsilea). The cell of the pollen- 

 granule extends itself into a tube of variable length (long in 

 Salvinia, shorter in Pilularia.). During the same time the cells of 

 the nucleus are developed near the apex of the embryo-sac, 

 become clearly distinguishable and laxer, filled with chlorophyll, 

 and at length break through the nucleus, so that they project free, 

 forming the nuclear papilla (mammilla nuclei). If a pollen-tube 

 now comes in contact with these cells, it penetrates deeply 

 between them until it reaches a layer of small green cells which 

 covers the embryo sac (Pilularia and Salvinia), and then it ex- 

 pands in a vesicular form, displacing the surrounding cellular 

 tissue, which, however, continues to be developed, and projects 

 from the seed-bud as a green body of variable size. In Salvinia it 

 forms two depending lateral processes, while in Pilularia a portion 

 of the superficial cells become elongated into capillary filaments. 

 In the vesicular extremity of the pollen-tube cellular ti^ue is 



