86 RE- GENERA TION 



of this interpretation he points out that in young prothallia of os- 

 munda, adventitious shoots do not appear, but in older plants, that 

 have become longer, these shoots may appear at the base, because 

 this region is no longer influenced by the apex, and consequently it 

 is possible for building material to accumulate at the basal end. 

 It may be granted that Goebel's idea is possibly correct, viz. that the 

 apex, or the apical end of a piece, may have some influence in pre- 

 venting the development of shoots at the base, but it does not follow 

 that this influence can be accounted for on the ground of a with- 

 drawal of building stuff from the basal part. As I shall attempt to 

 show in a later chapter, this influence may be of a different nature. 



It has been found by Pringsheim and others that pieces of the 

 stem of mosses may also produce new plants, and this holds even for 

 pieces of the stalk of the sporophore and of the wall of the spore 

 capsule (Fig. 10, A-D\ In this case, however, there is not produced 

 a new moss plant directly from the end of the piece, but threads or 

 protonemata grow out, as shown in Fig. 10, A, B, and from these 

 new moss plants are formed in the same way as on the ordinary 

 protonema. The threads that arise from the piece grow out from 

 single cells in the middle part of the stem. These cells are less dif- 

 ferentiated and are richer in protoplasm than are the other cells in 

 the stem. 



The prothallia of certain ferns are said by Goebel to regenerate if 

 cut in two ; at least this is true for the part that contains the vegeta- 

 tive point. In a piece without the growing point, the cells are very 

 little specialized, and the piece may remain alive ; yet it is incapable 

 of producing a new growing point. Comparing this result with the 

 power of regeneration possessed by lower animals, Goebel states l that 

 since in a plant new organs may arise without the typical form of the 

 plant being produced, "therefore, the completion of a leaf, for instance, 

 that has been injured, would be of no use to the plant, while in ani- 

 mals that do not have a vegetative point, the loss of an organ is a 

 permanent disadvantage in case the organ removed cannot be regen- 

 erated." The "explanation" of the difference in the two cases is 

 supposed, apparently, by Goebel, to depend on the usefulness, or 

 non-usefulness, of the regenerative act ! 



Brefeld has described several cases of regeneration in moulds. 

 There is produced from the zygospore of Mucor mucedo a germinat- 

 ing tube that forms at its end a single sporangium. If the tube is 

 destroyed or injured, a second one is formed from the zygospore, and 

 if this is injured a third time, a new tube is produced. Each time 

 the sporangium is smaller than in the preceding case. 



If the spore-bearing stalk of Coprinus stercorarius is cut off, the 



1 Goebel, '98, page 37. 



