NEW FORMATION OF ORGANS IN REGENERATION 



49 



tion adventitious shoots appear occasionally at the base also. Adventitious 



shoots may likewise arise on the base of the stalk of the gonophore if it 



is cut off from the thallus. and they may also spring from the walls of 



the gemmae-cups. Vochting explains this by the limited or unlimited 



growth of the organs concerned, but I take this to be an altogether 



superficial cause it would be superfluous to discuss his theoretical ideas 



and it seems to me that we shall more likely find the cause in either 



the direction of movement of the plastic material or in the wound-stimulus. 



The behaviour of the thallus of the liverworts is thus very instructive. 



We may connect the appearance of adventitious shoots at the base of 



the stalk of the gonophore in Marchantia with the fact that elongation 



continues there longest, and consequently the plastic material flows thither 



from above ; at the same time the polarity does not appear at all in 



others of the thallose liverworts, or not in the same amount, as in 



Marchantia J . The fact that in old portions of the 



thallus of Marchantia the polarity is obliterated 



gives special support to the explanation suggested 



here. The attractive influence of the vegetative 



point is very often limited and only extends to 



a certain distance from it. In young prothalli of 



Osmunda no adventitious shoots are found, but 



old ones which have reached a considerable length 



form them at their base which can no longer be 



influenced by the vegetative point (Fig. 20). A 



movement of material out of the posterior old 



part of a thallus of Marchantia towards its vegetative 



point cannot take place, or, if it does, only in a 



subordinate degree,and this determines its behaviour 



in regeneration. 



Brefeld 2 has made known a number of similar phenomena amongst 

 the Fungi. 



The zygospore of Mucor Mucedo usually produces in germination 

 one germ-tube, which, if the germination takes place in air, ends with 

 a sporangium. If this tube be destroyed before the capacity of the 

 spore for development is exhausted a second germ-tube grows out of 

 the zygospore, and if the spore be submerged in water a third appears, 

 and so on ; naturally, owing to the reduced amount of material available, 

 the sporangia on these tubes are successively smaller. The normal un- 

 branched sporophore may also be induced to branch by injury inflicted 

 upon it ; if, for example, in the course of its elongation it be covered by 



Fir,. 20. Osmunda regalis. 

 Prothalli. In the figure to 

 the right many ' adventitious 

 shoots ' are shown at the base 

 of the prothallus. Natural 

 size. 



1 See Schostakowitsch, 1. c. on preceding page. 



2 Brefeld, Untersuchvmgen ans dem Gesammtgehiete der Mykologie. 



r.OEBEI. 



