sect, i CRYPTOGAMS 



The SPORES are produced vegetatively in special receptacles termed 

 SPORANGIA, which occur on the asexual generation, either on the leaves, 

 or less frequently on the stems in the axils of the leaves. The spori- 

 ferous leaves are termed SPOROPHYLLS. The sporangium consists of a 

 wall composed of several layers of cells enclosing the sporogenous tissue, 

 the cells of which, becoming rounded off and separated from each other as 

 spore mother-cells, give rise each to fourtetrahedral spores (spore-tetrads). 

 The cells of the innermost layer of the sporangial wall are rich in 

 protoplasm, and constitute the TAPETUM. In the course of the 

 development of a sporangium the walls of the tapetal layer become 

 dissolved. The tapetal cells then wander in between the spore 

 mother cells, so that the spores eventually lie embedded in a muci- 

 laginous protoplasmic mass, the PERIPLASM, from which they derive 

 nourishment. Only the outermost layer of the wall is retained by the 

 mature sporangium. The spores are all unicellular. Each spore has 

 a wall composed of two coats, an EXINE, which is cutinised, and an 

 intine, consisting of cellulose. The spores of certain Pteridophytes 

 are invested by a second specially differentiated outer coat, the PER- 

 INIUM, which is divided from the protoplasm of the tapetal cells. 



The spores of the majority of the Pteridophytes have all the same 

 structure, and give rise on germination to a prothallium, which pro- 

 duces both antheridia and archegonia. In certain cases, however, the 

 prothallia are dioecious. This separation of the sexes extends in 

 some groups even to the spores, which, as macrospores, developed 

 in macrosporangia, give rise only to female prothallia ; or as MICRO- 

 SPORES, which are produced in microsporangia, develop similarly 

 only male prothallia. In accordance with this difference in the spores, 

 a distinction may be made between the HOMOSPOROUS and hetero- 

 SPOROUS forms of the same group ; but this distinction has no 

 systematic value in defining the different groups themselves, as it is 

 manifested to an equal degree in groups in other respects quite 

 distinct. 



Compared with the Bryophyta, the asexual cormophytic generation 

 of the Pteridophytes corresponds to the sporogonium, the prothallium, 

 on the other hand, to the Moss-plants with its protonema ; although 

 both groups may have originated phylogenetically from a common 

 ancestor, they have followed altogether different directions in the 

 course of their further development. The correspondence in the 

 structure of their sexual organs, in particular, points to the existence 

 of a relationship between them ; on the other hand, their asexual 

 generations exhibit the greatest disagreement, so that it would not 

 seem admissible to regard the asexual generation of the Pteridophytes 

 as derived from the sporogonium of the Mosses, although it is 

 manifestly homologous with it. 



The existing Pteridophyta are classified as follows : — 



1. Filicinae. — Ferns, stem simple or branched, with well-developed, 



