IN THALLOPHYTA 



149 



under conditions of dryness. Lemanea then behaves in this respect in the same way 

 as the Musci (Fig. 91). 



The 'pro-embryos' of Lemanea have been partly described as forms of the algal 

 genus Chantransia, and the same thing has happened in the case of the genus 

 Batrachospermum l . We may shortly summarize what takes place in this latter genus 

 in the following way : 



1. A pro-embryo composed of cell-threads arises from the germinating spore, 



and it clings at first to the substratum and thus prepares for its fixation 

 upon it. 



2. In normal conditions, of which abundant illumination is a prominent one, 



this pro-embryo usually attains only a small size ; upon it the characteristic 

 Batrachospermum-plants arise. 



3. Frequently however, especially in conditions of feeble illumination, the pro- 



embryo develops more luxuriantly, 

 tufts of erect cell-rows arise upon it 

 these have been described as species 

 of Chantransia and Batrachosper- 

 mum-plants may also develop upon 

 them, but if their primordia arise 

 at too great a distance from the 

 substratum they abort. 



4. The pro-embryos may propagate them- 



selves independently by means of 

 gemmae (gonidia). 



5. Secondary pro-embryos can develop 



from the cortical cells of the Batracho- 

 spermum-plant. 



Here then we see that the pro-embryos 

 are capable of an independent propagation, 

 and that they are able to grow under conditions 

 which do not suffice to call forth the higher form 

 of development of the plant ; these facts en- 

 tirely correspond with what is known in the case of the Musci. 



Of marine Florideae only two cases will be cited here : 



Dumontia filiformis 2 forms in germination an anchoring disc, consisting of 

 vertical rows of closely compressed cells, which clings closely to the substratum, and 

 resembles Hildenbrandtia, another genus of the Florideae. Upon the disc there is 

 developed a branched erect thallus which dies after producing the fructifications, 

 whilst the disc perennates and may produce new shoots of Dumontia. This then is 



FlG. 01. Lemanea torulosa? Thread-like 

 ' pro-embryo' upon which the plant destined to 

 produce the sexual organs arises as a cell-mass. 

 The condition is similar to what is found in 

 mosses. 



1 See Sirodot, Les Batrachospermes, Paris, 1884, and the criticism of his views in Flora, 

 1889, p. 5. 



3 Reinke, Algenflora der westlichen Ostsee. Kiel, 1889. Brebner, On the origin of the filamentous 

 Thallus of Dumontia filiformis, in Linnean Society's Journal, vol. xxx, p. 436. I think the endo- 

 gemtic origin of the thallus upon the disk, described by Brebner as a frequently occurring pheno- 

 menon, is due to its overgrowth at an early period of development. 



