124 GENERAL BIOLOGY 



protective outer wall, and the cell mass contained in it 

 finally develops into a very great number of minute round- 

 ish reproductive cells called spores, intermixed with sterile 

 cells called, because of their function, elaters. Upon the 

 drying and bursting of the sporangium wall, the elaters, by 

 their twisting and turning, assist in the scattering of the 

 spores. 



Alternation of generations. From those spores which, 

 when scattered abroad, find suitable lodgment and food for 

 growth, there develop new thalli, like the one with which 

 we started. Thus there are two distinct parts to the life 

 cycle of Conocephalus ; a large independently-feeding green 

 plant, which, because it produces the sex cells (gametes') is 

 called the gametophyte, and a small, dependent sporophyte 

 producing the spores. The former is a sexual, the latter an 

 asexual generation. This phenomenon is known as alter- 

 nation of generations. Because of its importance in the 

 green plant series, gametophyte and- sporophyte should 

 be clearly distinguished at once, the 

 former producing the eggs and 

 sperms, the latter producing the 

 spores ; the one regularly develop- 

 ing from the reproductive cells 

 produced by the other. 



Other Bryophytes. Riccia (fig. 

 FIG. 73. A spray of the liver- 7s) is a simpler liverwort, that has the 

 archegonia and antheridia immersed 



in the upper side of the thallus. Jungermannia (fig. 74) is a 

 liverwort of more highly specialized form, in which the midrib 

 of the thallus has become the plant stem, and the broad 

 margins have become differentiated into leaves. These, 

 however, are rather crude in form and simple in structure, 

 lacking veins and even a mid rib, and consisting of a 

 single layer of chlorophyll bearing cells. But they indicate 



