428 



SYSTEMATIC BOTANY. 



(sporogonium), which, in the course of its development, forms in an 

 asexual manner the spores, which in turn produce the sexual generation. 



When we compare the life-history of the Muscineee with that of Vas- 

 cular Cryptogams we find both a strong resemblance and a contrast. The 

 resemblance consists in this, that both follow the scheme of alternating 

 generations, one of which is endowed with sexuality and the other 

 purely asexual, so far as a process of impregnation is concerned. How 

 lav the so-called asexual generation of Cormophytal Cryptogams may be 

 sexually influenced by the other is a question on which we cannot enter 

 here. The contrast consists in the fact that whereas in the Mosses it is 

 the sexual generation which preponderates in the vegetative quality while 

 the asexual generation is the more transient one, in the Vascular Crypto- 

 gams it is the opposite which is true. There are, however, two cases, 

 one on each side (Anthoceros representing the Muscineae and Gymno- 

 yramme leptopliylla, Desv., representing the Vascular Cryptogams), in 

 which this rule is abandoned and the relations approach each other. Tn 

 the Gymnogramme it is the sexual generation (prothallium) which forms 

 the more persistently vegetating plant, while the growth of the asexual 

 (spore-bearing) generation scarcely exceeds that of the sporogonium of a 

 moss. In Anthoceros the sporogonium (asexual generation) shows a greater 

 vegetative tendency than is usually the case in the Muscinece, by continu- 

 ing to grow in the basal part and* produce here new spores after those 

 on the apical part are already ripe. These are exceptional cases ; but since 

 they occur in a perfectly normal manner they must be taken as consti- 

 tuting a form of alternation of generations intermediate between and 

 connecting those occurring in Vascular Cryptogams and Muscinese. 



Both Liverworts and Mosses 

 produce antheridia and arche- 

 yonia, either on the same plant 

 or on distinct individuals. There 

 are minor differences of structure 

 in the different groups of this 

 Orders, some of which may be 

 briefly described. 



The antheridia of the Hepa- 

 ticse (and with these agree the 

 same organs of Sphagnaceas) are 

 elliptical or globular sacs (fig. 

 497, c) formed of a single layer 

 of cells ; they are found im- 

 bedded in the thalloid stem of 

 Riccia, Pellia, &c., or in the sub- 

 stance of the (male) receptacles 

 of Marchantia (p. 434), or on 



Stalks arising from the frondose Antheridia and archegonia &c. of Hepati_8e: a 

 , T I j j.i vertical section of the inflorescence of Kadul 



Stem in loSSOmbroma, and in the 



axils of the leaves in the foli- 



aceous kinds rtJunyermanniete 



(fig. 497, ). Ihe Ulterior Of the c, immature antheridium of Eadula complanf/ta 



Sac IS filled with minute roundish < v ?rt. section), magn. 250 diam. ; d spermato- 



,-, , /. , i , T , ,,. zoid; e, immature trmt, with surrounding epigone 



Cells, at fiMt Coherent, but ultl- an d two abortive archegonia (/>/>), of Radulacom- 



mately free. These (the Sperm- planata (vert, section), magn. 100 diam. 



complcmata, with young (axillary) antheridia and 

 (terminal) archegonia, magn. 50 diam. ; b, vertical 



