672 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMS 



it exhibits in different genera of mosses varieties whose existence 

 and readiness of recognition render them characters of extreme value 

 to the systematic botanist, whilst they furnish objects of great 

 interest and beauty for the microscopist. The peristome seems 

 always to be originally double, one layer springing from the outer, 

 and the other from the inner, of two layers of cells which may be 

 always distinguished in the immature sporange ; but one or other of 

 these is frequently wanting at the time of maturity, and sometimes 

 both are obliterated, so that there is no peristome at all. The 

 number of the teeth is always a power ' of four, varying from 

 four to sixty-four ; sometimes they are prolonged into straight or 

 twisted hairs. The spores, or gonidial cells, are contained in the 

 upper part of the sporange, where they are clustered round a central 

 pillar which is termed the columel. In the young sporange the 

 whole mass is nearly solid (fig. 508, C), the space (I) in which the 



FIG. 512. Double peristome of 

 Brynm inter medi inn . 



FIG. 518. Double peristome 

 of CinclidiiDii nrcticunt. 



spores are developed being very small ; but this gradually augments, 

 the walls becoming more condensed, and at the time of maturity 

 the interior of the sporange is almost entirely occupied by the spores. 

 These are formed in groups of four by the binary subdivision of the 

 mother-cells which first differentiate themselves from those forming 

 the capsule itself. The capsule and seta of mosses together consti- 

 tute the organ known as the sporogone. 



The development of the spore into a new plant commences with 

 the rupture of its firm yellowish-brown outer coat or exospore, and 

 the protrusion of its cell-wall proper, or endospore, from the 

 projecting extremity of which new cells are put forth by a process 

 of outgrowth, forming a sort of confervoid filament known as the 

 protoneme. At certain points of this filament its component cells 

 multiply by subdivision, so as to form rounded clusters or buds, from 

 every one of which an independent plant may arise. The Musci, 

 therefore, present an example of the phenomenon known as alter- 

 nation of generations. The life-history of each individual may be 

 divided into two ' generations : ' the sexual generation or ' oophyte,' 



