772 PHYSIOLOGY. 



nent thallus of the Hepaticacese {figs. 811 and 813). Upon the 

 under surface of this structure we have ultimately formed, in the 

 Filices, both antheridia and archegonia ; but in the Eqidsetacece, 

 the antheridia and archegonia have only been found on separate 

 prothalli, and hence these plants would appear to be dioecious. 

 The antheridia {fig. 788) contain a number of minute cells called 

 sperm-cells {se), each of which contains a spirally wound ciliated 

 spermatozoid {sp). The archegonium {fig. 789) is a little cellu- 

 lar papilla, having a central canal, which when mature is open. 

 At the bottom of the canal is a cell called the embryo-sac, in 

 which a germ-cell or embryo-cell is developed. According to 

 other observers, this so-called embryonal cell is simply a germinal 

 corpuscle till after fertilization ; that is, a free primordial utricle, 

 without an external wall of cellulose. 



When mature, the upper part of the antheridium separates 

 from the lower, something like the lid of a box ; the sperm-cells 

 then escape, become ruptured, and emit their 

 1116. contained spermatozoids. These spermatozoids 

 make their way down the canal of the arche- 

 gonium to the embryo-sac, by which the con- 

 tained germ-cell, embryonal cell, or germinal 

 corpuscle, is fertilized. This germ-cell then 

 developes a pseudo-embryo, which soon pos- 

 sesses rudimentary leaves and roots {fig. 1116), 

 )h and ultimately produces a plant with fronds 

 bearing sporangia or capsules, which resembles 

 the parent from which the spore was originally 

 obtained. The Ferns and Horse-tails, as al- 

 ^?ora.Sf7rous^?ran! ready noticed (pp. 359 and 363), are thus seen 

 of a species of Pern to exhibit two stages of existence : in the first, 

 an^embrTo^produced the spores produce a thalloid expansion ; and in 

 by impregnation in the second, by means of antheridia and arche- 

 the protbliliium!^. gonia upon the sxirface of this prothallium, 

 there is ultimately produced a new plant, 

 resembling in every respect the one from which the spore was 

 originally derived. Hence Ferns and Horse-tails exhibit what 

 has been termed alternation of generations. 



2. Keproduction of Phanerogamous or C©tyledonotjs 

 Plants. — In all the plants belonging to this division of the 

 vegetable kingdom the male apparatus is represented by one 

 or more stamens, each of which essentially consists of an an- 

 ther enclosing pollen-grains {fig. 421,^); and the female, by 

 one or more carpels {figs. 425-427), in {fig. 427) or upon 

 {fig. 712) which one or more ovules are .formed. When the 

 ovules are contained in an ovary, the plants to which they belong 

 are called Angiospermozts ; but when they are only placed upon 

 metamorphosed leaves or open carpels, the plants are said to be 

 Gymnospcrmous. In the plants of both these divisions of the 



