446 BOTANY pakt ii 



ance with this difference in the spores, a distinction may be made 

 between the homosporous and heterosporous forms of the same 

 group ; but this distinction has no systematic vahie in defining the 

 different groups themselves, as it has arisen independently in several 

 groups. 



The con'espondence in the structure of their antheridia, archegonia, and 

 spore-motlier-cells is in favour of a relationship between the Bryophyta and 

 the Pteridophyta. Though both groups may have had their origin from a 

 common group of Algae, an independence in the further course of development 

 must be assumed in the two cases. Especially, it is impossible to derive the 

 sporophyte of the Pteridophyta from the sporophyte or sporogonium of the Moss. 

 While the latter without attaining any vegetative complexity comes to an end 

 early with spore-formation, the Fern sporophyte develops into a massive embryo 

 within the archegonial venter, and this becomes differentiated into stem, leaf, and 

 root. Tlie vascular bundles appear as quite new structures, the possession of 

 which enables the sporophyte to proceed to the development of a large complicated 

 and sometimes tree-like terrestrial plant ; this contrasts with the Bryophyta, where, 

 owing to the simple cellular structure and the absence of special water-conducting 

 channels, no great size can be reached. The plant only proceeds at a late stage to 

 the production of spores. The spore-mother-cells are formed endogenously in special 

 parts of the leaf; these are indeed called "sporangia," but are not homologous 

 with the sporangia of Thallophyta. On this account it would seem advisable to 

 use a new term for the so-called sporangia of Pteridophyta (sporothecae). The 

 spore-mother-cells, which may be most closely compared with the tetrasporangia 

 of Brown Algae, correspond rather than the sporothecae to the sporangia of 

 Thallophyta. 



The gametophyte of the Vascular Cryptogams closes its development early by 

 the formation of sexual organs. The typical fern-prothallus hardly surpasses the 

 youth-form of a thallus, while in the Bryophyta, on the other hand, the sexual 

 generation exhibits a progressive development C"^). 



The existing Pteridophyta are classified as follows : — 



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

 developed, alternate, often deeply divided or compound leaves called 

 fronds. Sporangia either on the under side of the sporoi)liylls, 

 united in sori or free, or enclosed in special segments of the leaves. 



Sub-Class 1. Filicinae eusporangiatae. — Eipe sporangia with firm 

 wall composed of several layers of cells. Homosporous. 



Sub- Class 2. Filicinae leptosporangiatae. — Ripe sporangia Avith 

 walls one layer thick. 



Order 1. Filices. — Ferns, in the narrower sense. Homosporous. 

 Order 2. Hijdropterideae. — AVater-Ferns. Heterosporous. 



2. E(2imetinae. — Horse-tails. Stem simple or verticillately branched, 

 with whorled, scale-like leaves forming a united sheath at each node. 

 Sporophylls peltate, bearing a imraber of sporangia on the under side, 

 and aggregated into a cone at the apex of each fertile shoot. 



