1891.] en British Mosses, 243 



have endeavoured to exhibit many of these modes of reproduction, 

 dividing them into those cases in which it takes place with protonema, 

 and those cases in which it takes place without. 



Weismann's Theory. — The consideration of this table is not without 

 its interest in reference to Prof. Weismann's theory of the division 

 of the cells and plasma of organisms into two kinds : the germ cells 

 and germ plasma endowed with a natural immortality, and the 

 somatic cells and somatic plasma with no such endowment. That the 

 mosses are a difficulty in the acceptance of the theory as a universal 

 truth, the Professor himself admits. The evidence of the mosses 

 seems to amount at least to this: that in this whole group, the 

 highest in this line of development, where the oophytic generation 

 produces the principal plant, and where there are highly specialised 

 organs for the production of spores or germ cells— that in this whole 

 group either there is no effectual separation between the two kinds of 

 plasma, or that the germ plasma is so widely diffused amongst the 

 somatic plasma that every portion of the plant is capable of repro- 

 ducing the entire organism. 



Comparison with Zoological Embryology. — The table will further 

 offer us some points of comparison with animal embryology. 



In that branch of physiology, one of the most remarkable facts is 

 what has been called recapitulation, i. e. the summary in the life of 

 the individual of the life of the race, so that the development of the 

 individual tells the development of the race — e. g. the gills of the tad- 

 pole tell us of the descent of the Batrachians from gill-breathing 

 animals. 



So here we cannot doubt that the protonema of the moss tells us 

 of the descent of the whole group of mosses from the Algae. 



Another remarkable fact in animal embryology is the co-existence 

 in exceptional cases of the mature and the immature form ; so the 

 axolotl retains both gills and lungs throughout its life. In like 

 manner it happens with some mosses, e. g. the Phascum, retains its 

 algoid protonema throughout its life. 



Again, in zoological embryology, an attempt is often found, to 

 use the language of Prof. Milnes Marshall,* " to escape from the 

 necessity of recapitulating, and to substitute for the ancestral process 

 a more direct method." 



In like manner the preceding tables will show to how great an 

 extent Nature has adopted the system of short-circuiting in the re- 

 production of the mosses ; for in every mode of reproduction, except 

 that through sporogone and spore, it will be observed that a 

 shorter circuit is travelled, e.g. the Orthotrichum phyllanthum pro- 

 duces cells at the end of its leaves, which, falling to the ground, 

 throw out a protonena which produces a bud, and then a moss plant, 

 and then a cell at the end of the leaf, and the whole sporophytie 



* Addresa to Biological Section of British Association (' Nature,' vd. xlii, 

 p. 478). 



