CELL-DOMINIONS IN THALLOPHYTA 



39 



It is of interest that three other plants growing in the same locality as the 

 one just mentioned present a quite similar differentiation of their organs. Bostry- 

 chia callipteris has fixing shoots like those of Bostrychia Moritziana; in Lomentaria 

 impudica the shoots for attachment stand upon the under side of the branch-system 

 between two lateral shoots and are not unfrequently provided with outgrowths ; 

 Delesseria Leprieurii forms no twigs as shoots of attachment, but produces tufts 

 of rhizoids just below each apparent fork of the thallus which perform the same 



FlG 14. Bostrychia Mortiziana. Habit of a shoot. The shoot-axis bears branched short shoots which serve as 

 organs of assimilation, and unbranched shoots, W, turned to the substratum by which the plant is fixed. Magnified. 



work, and they are absent from the shoots which bear tetraspores. In all these 

 cases the organs of attachment arise without the influence of an external stimulus, 

 shoots for this definite purpose are laid down as such; but in Plocamium (Fig. 15) 

 the development of a shoot into a fixing organ depends entirely on whether its 

 apex comes into contact with a fixed body or not. 



Here then also through simple stages of formation of organs a differentiation 

 comes about which represents the root 1 and leafy shoots of the higher plants. 

 This similarity is all the more striking when the short shoots take on an external 

 leaf-like appearance. Polyzonia jungermannioides, for example, shows, as its specific 



\ In Bostrychia Moritziana the down-growing twigs are the analogues of roots. 



