REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



242 



every respect, those of the Ferns. The anthe- 

 ridia of the Equisetaceae are placed, not upon 



Antheridia of Equisetum, 300 diam. 

 c, ripe antheridium, from which the antherozoids 

 are beginning to escape ; b, unripe autheridium. 

 (Hofmeister.) 



the inferior surface, but along each margin of 

 the principal branch of the prothallium.- 



88. Archegonium. The archegonia were 

 first discovered and figured by Milde* in 

 Equisetum Telmateia, and have been since 

 more completely described by Hofmeisterf and 

 BischofF;}: in two other species. The pro- 

 jecting papilliform portion consists, according 

 to the last-mentioned observer, of eight cells, 

 of which the four lower, in apposition to each 

 other, have the general form of truncated 

 cones, each presenting two flattened surfaces 

 by which it is united to its two neighbours. 

 The upper, in the same relation to each other, 

 are nearly cylindrical, but are slightly rounded 

 at their summits. The axis of the organ is 

 occupied by a quadrilateral intercellular 

 passage. The whole is supported on a base, 

 which consists of two or three rows of cells 



Fig. 171. 



superimposed upon each other, which com- 

 bine to form a circular wall round a central 

 cavity, which contains the germ, and is the 

 termination of the quadrilateral canal. On 

 the transformation of the germ-cell into the 

 embryo, observations are as yet wanting. 



89. Spores and sporangia. The organs upon 

 which the spore-cases are supported are ar- 

 ranged in whorls round the upper part of 

 the fruit-bearing stem. They seem to be 

 modifications of the ordinary stem-leaves, on 

 which account they have received the name 

 of sporophylla. In its earliest condition, the 

 sporophyllum is a cellular projection of the 

 surface ; but, as it advances towards maturity, 

 it assumes the form of a hexagonal disc 



Fig. 172. 



Archegonium of Equisetum Telmateia, 200 diam. 

 The axial canal terminates in a spherical cavity, 

 which is deeply embedded in the tissue of the 

 prothallium, and contains the germ-cell. (Bi- 

 schoff.) 



* Zur Entwick. der Equiseten. Bot. Zeitung 

 St. 32, 1852. 



f Beitrage zar Kenntnisse der GefUsskryptogamen 

 (referred to by Bischoff in the following paper.). 



J Ann. des Sc. Nat. 3 me S. t. xix. p. 234. (Ex- 

 tract from Bot. Zeitung, St. 6. Feb. 1853.). 



Vertical section of one of the sporophylla of Equi- 

 setum limosum, 100 diam. 



a, mature sporangium ; b, another in outline. The 

 capsule of the sporangium is composed, when 

 ripe, of the external layer of cells only, in conse- 

 quence of the absorption of the two inner layers, 

 which resemble in their structure those described 

 more at length in the sporangium of Selaginella 

 ( 94.), and seem destined to afford the ma- 

 terials for the rapid growth and development of 

 the mother cells of the spores. 



attached by a pedicle at its centre. Upon the 

 surface of the disc which faces the stem, 

 the spore-cases are formed. Each spore-case 

 originates as a little papilla, and consists of a 

 large central cell, which is invested by a 

 single layer of others of smaller size. As the 

 organ enlarges, these last are transformed 

 into a capsule consisting of three concentric 

 layers, within which is enclosed a mass of 

 cells exhibiting large central nuclei and 

 grumous contents. In each of these cells 

 the nucleus is afterwards replaced by two 

 others similar to it, which almost fill the 

 cavity. These, however, soon disappear, and 

 now four globular nuclei, much smaller than 

 their predecessors, present themselves, and 

 are arranged, as in the Hepaticae, towards 

 the four angles of a regular tetrahedron. 

 Around each nucleus a tetrahedral cell is 

 formed, within which, after it has become 

 detached from its fellows, there is deposited 

 on the inner surface of its membrane, a 

 gelatinous transparent layer. Within this 

 layer, and immediately surrounding the 

 nucleus, may be distinguished the primordial 

 vesicle, on the surface of which the cellulose 

 membrane of the future spore is secreted, as 

 well as the two parallel, elastic fibres by 

 which it is surrounded. When the spore is 

 ripe, these last, which are external to the 



