INTRODUCTION TO C'llYPTOGAMIC BOTANY. 423 



few words. The spores of all germinate or undergo a j^rocess 

 of cell-formation, homologous with germination, though no 

 threads or external organs are protruded. In the one case, 

 after a time, plants are formed upon the germinating threads, 

 which are, in fact, of the same nature as a mycelium, or the 

 plant is formed without any distinct mycelioid condition ; in 

 the other case, a body is generated of various forms, called a 

 prothallus, which answers the same purpose as the perfect 

 plant in the former, so that the prothallus in the one case is 

 homologous with the plant in the other. In both alike, urn- 

 shaped cavities called Archegonia appear, from a privileged 

 cell of which, after impregnation, a sporangium is formed in 

 the one case, and in the other a plant capable of producing 

 sporangia. Perennial Musci and Hepaticco so far agree with 

 Phamogams, that there is a fresh crop of fruit each year ; but 

 then the result of impregnation is not a seed, but an organ, 

 which produces the reproductive bodies or spores, much after 

 the fashion in which pollen grains are generated. Ferns and 

 Clubmosses, though living to a hundred years, and producing 

 a crop of spores each year, are impregnated but once, and that 

 before the plant has assumed its true habit. The result of 

 impregnation in these is something more or less resembling the 

 embryo of a Phrenogam, and, like that, produces by progres- 

 sive development a perfect plant.* 



466. As regards classification, we have three distinct groups 

 into which Acrogens are divisible : 1, Those in which the 

 single spore is, in all probability, immediately impregnated, 

 and in which there is no prothallus, as CharacecB ; 2, Those in 

 which the whole plant, whether annual or biennial, is the 

 immediate parent of the fruit, the result of impregnation being 

 the production of fruit from an embryonic cell, as in Musci 

 and Hepaticm ; and 3, Those in which the result of impreg- 

 nation is a new plant, whether annual or perennial, producing 

 one or more successive crops of fruit, as Filiccs. 



* Illustrative figures will be given uuder the res2)ective orders, wliioli 

 may be consulted in explanation of tlie terms here used. 



