48 GENERAL DIFFERENTIATION OF THE PLANT-BODY 



regeneration of the mosses a new plant is not produced directly, but a 

 protonema is first of all formed from which the plant arises, in the same 

 way as the juvenile stage of the plant is developed from germination of 

 the spore x . This is usually not the case in the liverworts. Even in the 

 forms which develop a germ-tube from the spore in germination there 

 is usually produced in the first instance upon detached leaves and other 

 parts a cell-mass, and upon this the primordium of a new plant afterwards 

 appears 2 . More accurate experimental examination of these differences 

 is yet required. I believe that it is possible so to influence the leaves 

 that in their regeneration the same phenomena will appear as are seen 

 in the germination of the spore. 



I may here cite a few particulars of the phenomena of propagation 

 in Bryophyta. 



In the foliose liverworts adventitious shoots arise, often in great 

 numbers, upon severed leaves, but there is no preference shown for the base 

 of the leaves as a point of origin. Here then is a difference between the 

 leaves of liverworts and those of higher plants, for in the latter new 

 formations always appear at the base, and I would attribute it to the 

 fact that when the leaves of the liverworts, which consist of one layer 

 of cells only, are cut off, the plastic material which was flowing to the 

 shoot-axis collects at the base of the severed leaves in so small amount 

 that they have not enough for the formation of adventitious shoots ; 

 plastic material can only be formed through the activity of assimilation 

 in the severed leaves, and therefore regeneration remains in abeyance in 

 the dark and also if the air be free of carbonic acid, because in both 

 cases assimilation is impossible. There is no reason for a preference of 

 the leaf- base in leaves in which plastic material is manufactured only 

 after they have been severed, whilst in leaves which are rich in contents 

 and possess a midrib, as is the case in some mosses, phenomena similar 

 to those observed in the leaves of Spermaphyta may appear. 



Amongst the thallose liverworts the behaviour of Marchantia has been 



o 



thoroughly studied 3 . If a portion be cut out of a thallus by a transverse 

 cut, adventitious shoots are only formed on its apex, that is to say, upon 

 the side of it which was turned to the vegetative point of the uninjured 

 plant ; even small fragments of the thallus are quite capable of regenera- 

 tion. With increase of age however the opposition between apex and 

 base decreases, and if a quite old portion of a thallus be used for regenera- 



1 In Sphagnum, for example, a protonema-thread develops from severed pieces of shoot and it 

 soon passes over into the flat protonema characteristic of the genus. I have not yet succeeded in 

 obtaining regeneration from detached leaves of Sphagnum. 



2 See Schostakowitsch, Uber die Reproduction und Regeneration bei den Lebermoosen, in Flora, 

 Ixxix (Erganzungsbd., 1894"); Goebel, Uber Jugendformcn von Prlanzen und deren kiinstliche 

 \Yiederhervorrufung, in Sitzungsber. der k. bayer. Akad. d. Wissensch., 1896. 



s Vochting, Uber die Regeneration der Marchantien, in Pringsh. Jahrb. xvi (iS6j;\ p. 367. 



