DIV. i THALLOPHYTA 367 



are unicellular structures which become separated from the parent plant, 

 and form the starting-point of the development of a new individual. 

 The Cryptogams might, therefore, be termed spore-bearing plants. The 

 seed-plants also produce spores, but the sporangium and contained spore, 

 which as a special structure develops into the seed, continues its 

 development while still connected with the parent plant, the seeds 

 being ultimately separated from this. 



The distinctions between the Thallophytes, Bryophytes, and 

 Pteridophytes are briefly the following : 



The THALLOPHYTA include a great variety of plants, the 

 vegetative portion of which may consist of one or many cells in the 

 form of a more or less branched thallus. Reproduction is both 

 sexual and asexual, but there is usually no definite succession of the 

 two modes of reproduction. An alternation of generations only 

 appears in the higher forms. 



The BRYOPHYTA and PTERIDOPHYTA exhibit a regular alternation 

 of two generations in their life-history. The asexual generation forms 

 spores, and is called the SPOROPHYTE. From the spore the sexual 

 generation or GAMETOPHYTE develops; this bears sexual organs of 

 characteristic construction, the male organs being called antheridia, 

 and the female organs archegonia. From the egg-cell contained in 

 the latter, after fertilisation, the sporophyte again arises. 



In the BRYOPHYTA the plant body is always a thallus, although in 

 the higher Mosses there is a segmentation into stems and leaves. The 

 Bryophytes possess no true roots, and their conducting bundles, when 

 present, are of the simplest structure. The sporophyte is a stalked 

 or unstalked capsule, which lives semi-parasitically on the sexual plant. 



The PTERIDOPHYTA have small thalloid gametophytes ; the sporo- 

 phytes exhibit a segmentation into stems, leaves, and roots, and also 

 possess true vascular bundles ; they thus resemble the Spermato- 

 phyta in structure. 



The Bryophyta and Pteridophyta are united as the Archegoniatae on account 

 of the structural agreement in their female reproductive organs or archegonia. 

 These organs are also present in a somewhat simplified form in the lower Spermato- 

 phyta (in most Gymnosperins), so that a sharp line cannot be drawn between the 

 Archegoniatae and higher groups of plants. 



I. THALLOPHYTA (^ 



It was formerly customary to divide the Thallophyta into 

 Algae, Fungi, and Lichens. The Algae are Thallophytes which 

 possess chromatophores with pigments, particularly chlorophyll ; 

 they are, therefore, capable of assimilating and providing inde- 

 pendently for their own nutrition (autotrophic). The Fungi, on the 

 other hand, are colourless and have a saprophytic or parasitic mode 



