80 



CRYPTOGAMOUS TYPES. 



to grow upwards, developing the slender stalks (setee) 

 with the capsules at the summit, and surrounded by the 

 calj'ptra, which is, in fact, nothing but the wall of the 

 archegonium which is torn away at its base and carried 

 upwards. Then the spores are developed around the 

 columella, and the round of life of the plant is completed. 

 As in the Ferns, we have here also exhibited an alternation 

 of generations, the one generation being that arising from 

 the development of the spore and resulting in the proditc- 

 tion of the antheridia and archegonia ; the other being 

 that arising from the fertilization of the special cells in 

 the archegonia, and resulting in the production of spores. 



Liverworts. 



Figs. .')10 and 311 are representations of portions of a very 

 common Liverwort, Marchantia poli/viorpha. It may 

 be found growing along the borders of marshes and in 

 wet places generally, often with intermingled moss. It 

 is of a deep green colour, and usitally spreads over a con- 

 siderable extent of surface. There is no appearance of 

 leaves, the plant-body lying flat upon the surface upon 

 which it grows,' and putting forth root-hairs on the under 

 side. From the upper side arise peculiar stalked bodies of 

 two sorts, as shown in the figures ; the one consisting 

 of flattened or slightly convex disks, and the other being 

 star-shaped. These stalked bodies contain the reproduc- 

 tive organs. In cavities on the upper surface of the flat- 

 tened disks are prodttced the antheridia, from the cells of 

 which are liberated the antherozoids. On the under sur- 

 face of the rays of the star-shaped bodies are produced 

 clusters of flask-shaped archegonia, each with a germ-cell 

 at its base, and fertilization takes place in the manner 

 already described in the account of the Moss. As a result 

 of fertilization, a capsule is developed which, produces 

 spores, pretty much as in the Mosses, though in Mar- 

 chantia the stalk of the capsule is very short, and the 

 whole is surrounded by a loose sheath which, grows tip 

 from the base and at length completely encloses it. The 

 spores on germinating develope ii^to plant bodies such as 

 we have described, so that the alternation of generations 

 is here also well marked. 



Other Liverworts more nearly resemble the Mosses in form, 

 having leafy stems, from the summit of which arise 

 slender stalks with, capsules at the upper end. These 

 capsules, however, do not open by a stoma, but are four- 

 valved, and at maturity the valves split asunder, allow- 

 ing the escape of the spores. In the leaves of these hitter 

 forms there are no veins of any kind. Forms in which 

 the plant-body is a flat expansion, as in Marchantia, are 



Fig. 309. 



Vis:. 310. 



