62 



REGENERATION 



and 48 give the result of such an experiment. The apex of the 

 stem in this case was dipped into water, but this is not necessary. 

 Figure 47 shows the result after 8 days. Three nodes had formed 

 roots and the three most apical nodes had commenced to form 

 shoots. Ten days later (Fig. 48) only the most apical shoots had 

 continued to grow, thereby suppressing the shoots that had com- 

 menced to grow in the other nodes. The roots at the extreme 

 base of the stem had now commenced to grow and the other 

 roots had wilted. In Figs. 47 and 48 everything happened in the 



Fig. 48. — Same stem as in Fig. 47 10 days later. Roots have formed at the 

 base and shoots in apex, just as in stems suspended in upright position. 



inverted position of the stem as it did in the upright position in 

 Figs. 43 to 45, and gravity has therefore little if anything to 

 do with the polar character of regeneration in a stem of Bryophyl- 

 lum calycinum in vertical position. We shall see later that it is 

 different when the stem is suspended horizontally. 



The polar character of regeneration can be obliterated when 

 the stem is put partly under water. It is in this case necessary 

 that one of the two ends of the stem should be in air, since other- 

 wise regeneration may fail to occur. When a whole defoliated 



