CRYPTOGAMS AND PHANEROGAMS. 239 



Gymnospermce is given to them. In the higher Flowering-plants, 

 the Angiospermce, the ovules are distinctly situated on the edge, the 

 upper surface, or base of the carpel ; but the carpel closes round 

 the ovules which are therefore enclosed in a chamber the ovary. 

 In a few cases, for example in the Polygonacese, an ovule is situated 

 apparently on the apex of the stem itself, as in the Yew ; in other 

 cases, as in the Primulaceae, many ovules are apparently devel- 

 oped on the apex of the stem, which seems to have been speciallv 

 adapted as a placenta, but it is also possible and correct in these 

 cases to suppose that the ovules are in reality developed on 

 the carpels. 1 A single fully-developed carpel or a collection of 

 carpels joined together is termed the pistil. The extremity of the 

 carpel, which is specially developed to catch the pollen-grains and 

 form a suitable nidus on which they may germinate, is called the 

 stigma. The united edges of a carpel which bear the ovules are 

 termed the ventral suture. The back of the carpel forms the dorsal 

 suture. The Marsiliacea? take a position among the Hydropteridere 

 analogous to that occupied by the Angiosperms; the sporangia are 

 in a corresponding manner enveloped in a closed leaf. 



The collection of stamens in a flower is termed the androecinm, 

 and all the carpels, whether individually free or united into one 

 pistil, the gynceceum. 



The Sporangia. The asexual generation of the Mosses is the 

 sporogonium, in which the spores arise in tetrads from the mother- 

 cells. The sporangia in the FiUcince take their origin either from 

 a single cell (Leptosporangiata?) or, what probably may be regarded 

 as an older stand-point, from a group of cells (Eusporangiata 1 ). In 

 both cases there may be distinguished in a mature sporangium 

 three tissues, which have different significance (Fig. 204) : (1) an 

 external layer, the sporangium-wall, most frequently composed of 

 one layer of cells made up of cells of dissimilar structure, so that on 

 desiccation the wall is ruptured and the sporangium opens in a 

 definite manner; (2) an internal group of cells, consisting of the 

 spore-inother-cells, developed from an archesporium, and which by 

 division into four gives rise to the spores ; (3) a layer of cells 

 lying' between the two already mentioned, which is dissolved before 

 maturity. The intermediate cellular layer, which directly sur- 

 rounds the spore-forming cells, is in form and contents more worthy 

 of note than the others, and is termed the tapetum. The construc- 



1 It may be here remarked that another explanation is possible, based on the 

 study of the development (A") . 



