368 ORGANOaRAPHY. 



a striking similarity to pollen. It must be noticed, however, 

 that spores, although similar in structure to pollen, perform 

 essentially different functions. The threads which are thus pro- 

 duced by the germination of spores, may either reproduce the 

 plant directly; or give rise to an intermediate body of varying 

 form, called tho, pro-thallus or pro-embryo {Jig. 784, p), from which 

 the fructiferous or fruit-bearing frond or stem ultimately springs. 



Although Cryptogamous Plants have been thus described 

 above as destitute of an embryo, yet it must be admitted that the 

 spores of some of these plants do contain an analogous body, — 

 that is to say, they contain a body which has all the elements of 

 the future plant in a rudimentary state. Kuch spores are, how- 

 ever, of but I'are occurrence, and the rudimentary plant which 

 they contain is of so different a nature from the true embryo of 

 Phanerogamous Plants, tliat such exceptional cases can scarcely 

 be said to interfere materially with the character given above. 



Such are tlie chief distinctive characters in the reproductive 

 organs of Cryptogamous and Phanerogamous Plants. The nature 

 of these oi-gaus in the different tribes of flowerless plants, are 

 however, so remarkable, that, in order to make ourselves ac- 

 quainted with them, it will be necessary for us to describe the 

 peculiarities of each separately. 



The Cryptogamous Plants have been divided by botanists into 

 two great divisions, called respectively Acrogens and Tkallugens, 

 the characters of which will be described hereafter, when treating 

 of Systematic Botany ; but it will be better for us to keep these 

 two groups in view in our sketch of the reproductive organs of 

 flowerless plants, and hence we shall treat of them under those 

 two heads. 



Section 1. — Reproductive Organs of Acrogens. 



Acrogenous Plants have been also divided into several sub- 

 divisions, called Natural Orders or Families; these are the 

 Filices, Equisetacea, Marsileacece, Lycopodiacece, Musci, Jlepa- 

 ticacece, and Characece. The general characters of these orders 

 will be described under their respective heads in Systematic 

 Botany ; — the nature of their reproductive organs have now 

 only to be described. 



1. Filices or Ferns. — The fructification of these plants 

 consists of little somewhat rounded cases, called capsules, 

 sporangia, or iheca {fig. 780, sp), springing commonly from the 

 veins on the under surface or back of the leaves or fronds {figs. 

 780 and 781), and containing spores in their interior. In a 

 very few cases sj)orangia have been observed on the upper 

 surface, as in Acrostichuui. The sporangia arc arranged in 

 little hcajjs, wliich vary much in form, called sori {figs. 780 and 

 781, i), and arc either naked, as in Polypodium {fig. 780), or 



