REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



this manner it becomes firmly implanted, tlie 

 tissue which surrounds it assuming the form 

 of a sheath, and receiving the name of vagi- 

 nnla. During this process, the dilated portion 

 of the archegonium has increased in size, and 

 has now attained about ten times its original 

 length. Finally, it gives way at its line of 

 junction with the vaginula, and is carried up- 

 wards on the summit of the still lengthening 

 fruit. 



77. Development of the spores. The upper 

 portion of the cylindrical fruit, which is des- 

 tined to become the capsule, begins, some 

 time after the calyptra has given way, to dilate 

 rapidly. Soon after there is formed, by the 

 separation of the external and superficial lay- 



Fig. 166. 



Section of half -ripe fruit of the same, 50 diam. 



The globular dilatation exhibits the following 

 parts : a, the capsule. Within this, and 

 separating it from the central portion, is a dark 

 space, which corresponds to a cavity of the 

 form of a hollow cylinder ; b, columella ; c, super- 

 ficial layer of central portion ; d, remains of 

 archegonium; e, vaginula. (From fig. 164 to 166 

 from Hofmeister.) 



ers of cells from the central portion, a cavity 

 of the form of a hollow cylinder, the axis of 

 which coincides with that of the fruit. At 

 this stage, the central portion consists of an 

 axile column of large cells, closely invested by 

 a single layer of smaller ones (the columella) ; 

 a superficial layer of cells, about four times as 

 large as those last mentioned ; and Lastly, 

 between the two, a layer of nucleated cells, 

 with granular contents, the primary parent 

 cells of the spores. The development of these 

 last consists in the disappearance of the nu- 

 cleus of each, and the substitution for it of 

 two others ; this being accompanied or fol- 

 lowed by the division of the primordial mem- 

 brane into two new vesicles, each of which 

 encloses a nucleus. A cellulose membrane is 

 now formed at the surface of contact of the 

 two vesicles by which the original cavity is 

 bisected. In the cavity of each of the result- 

 ing nucleated cells, two new ones make their 

 appearance, apparently by contraction of the 

 primordial membrane, either before or inimc 1 - 



239 



diately after its division into two halves. On 

 the surface of each half cellulose is secreted, 

 so that the spherical cells which are thus 

 formed possess a delicate cellulose external, 

 and a very distinct inner membrane (primor- 

 dial vesicle.) This last divides into four por- 

 tions (the young spores), each of which 

 becomes invested with a layer of cellulose. 

 The ripe spore has been already described. 

 The capsule now gives way at the line of its 

 insertion on the pedicle which supports it. 

 It is by the opening thus produced that the 

 spores make their escape after the dislocation 

 of the layers of cells immediately surrounding 

 them. Phascum differs from all other genera 

 in the absence of all trace of an operculum. 



78. Ferns. No two plants could be found 

 which differ more completely from each other 

 in the appearance which they present to the 

 ordinary observer, than a Hepatica and a Fern, 

 at the moment that the spores of each arrive 

 at maturity ; yet, in the history of their organ- 

 isation and development a very close corre- 

 spondence exists. The immediate result of 

 the germination of the spore of a Fern is a 

 frond similar to that of the simpler forms of 

 Hepatica ; on this frond antheridia and arche- 

 gonia are formed. In each fructified arche- 

 gonium, a central germ-cell is developed to a 

 new individual, widely different in organisation 

 from the parent. It, in its turn, produces 

 spores, the germination of each of which is the 

 commencement of a new circle of phenomena 

 similar to the one which precedes it. Dividing 

 this circle into two periods, as before, we have 

 the following stages in the development. 



79. First period.* Germination of the spore. 

 The mature fern-spore consists of a delicate 

 transparent vesicle, which is invested in a 

 brown resistant external membrane. Germi- 

 nation consists in the budding out of the trans- 

 parent vesicle so as to form a nipple-shaped 

 projection, which penetrates the external mem- 

 brane. The projecting part divides repeatedly 

 by transverse septa. About the same time a 

 second budding out takes place in the oppo- 

 site direction, which is destined to the forma- 

 tion of a root. By the further growth of new 

 cells, a flattened two-lobed organ is formed 

 the Prothallium. 



Fig. 167. 



Early condition of p/ut/iatlium of Gymnogramma 

 chrysophylla, about 20 diam. (Henfrey.) 



80. The antheridia. The antheridia are situ- 

 ate on the under surface of the prothallium, 



* Hofmeister, /. c. pp. 78 82. 



