204 BOTANY 



the Bryophytes arise from the blepharoplast, which is of cytoplasmic 

 origin. When the spermatozoids escape, the remaining cytoplasm of 

 the mother-cell adheres to the end, as a small vesicle. 



The walls of the sperm-cells become mucilaginous at maturity, and 

 the dehiscence of the antheridium is due to the swelling of this 

 mucilaginous matter, when water is applied. 



Sporophyte 



The fertilized egg becomes at once invested with a cellulose mem- 

 brane, and grows until it completely fills the cavity of the venter. 

 The development of the sporophyte in the Liverworts is not always 

 the same. In the simplest type, that of Riccia (Fig. 171), all but a 

 single superficial layer of cells constitutes the archesporiuin of the 

 globular sporophyte, and all the archesporial cells give rise to spores. 

 In all other forms there is a greater or smaller amount of sterile 

 tissue in the sporophyte. In the Anthocerotales, especially the 

 genus Anthoceros, the sporophyte becomes very complicated. A 

 distinct system of green assimilative tissue, with stomata, is devel- 

 oped, and the archesporium is relatively small. 



As the embryo grows, the venter of the archegonium also shows 

 active growth, and, except in the Anthocerotales, the sporophyte is 

 retained within the venter of the archegonium, now known as the 

 " Calyptra," until the spores are ripe. Then by a sudden elongation 

 of the stalk, or " Seta," of the sporophyte, it breaks through the 

 calyptra, and carries up the spore-bearing capsule at the top, soon 

 shedding the spores. 



In most of the Liverworts certain cells of the archesporium remain 

 undivided, and develop into spindle-shaped cells, upon whose walls 

 are developed spiral thickenings, which are strongly hygroscopic. 

 These cells are the Elaters (Fig. 160, C), and it is probable that they 

 are of assistance in breaking open the capsule containing the spores, 

 and possibly the hygroscopic moveiiients may also be useful in scat- 

 tering the spores after they are shed. The wall of the capsule, or 

 upper spore-bearing portion of the sporophyte, often shows similar 

 thickenings upon the walls, and these are also instrumental in open- 

 ing the capsule. 



In all Liverworts except the Ricciaceae, the base of the sporophyte 

 forms a bulblike organ, the Foot (Fig. 160, A, /), whose cells are in 

 close contact with the adjacent cells of the gametophyte, from which 

 it absorbs water and food for the needs of the growing sporophyte, 

 which is thus parasitic, as it were, upon the gametophyte. 



The Spores. The ripe spores of the Liverworts are tetrahedral 

 cells, with a double or triple outer wall and dense contents. Where 

 the spores can germinate at once, as in most forms from the moist 



