74$ 



ECOLOGY 



possess erect or orthotropic and horizontal or plagiotropic shoots, which 

 obviously are correlated, since the removal of the former causes the 

 latter to become erect; the presence of the 

 erect shoot appears to inhibit the horizontal 

 shoot from becoming erect. The reference 

 of phenomena to correlation, or for that 

 matter to inherent factors, does not explain 

 them. The use of such indefinite terms is 

 mystifying rather than illuminating, and ex- 

 planations must be sought in actual under- 

 lying causes. However, terms like correla- 

 tion and inherent causes may be useful 

 temporarily, as serving to denominate these 

 particular regions of our ignorance. 



Regeneration. In most plants the termi- 

 nal buds are stronger than the others, and 

 they develop into vigorous shoots (figs. 952, 

 953); the upper lateral buds develop into 

 less vigorous shoots, and the lower lateral 

 buds usually remain undeveloped. Such 

 plants are characterized by excurrent branch- 

 ing. In some cases (as in the lilac) the lateral 

 buds are the stronger, and their continued 

 development results in deliquescent branch- 

 ing. If a terminal bud of an excurrent shoot 

 is injured or removed during development, 

 one or more lateral buds, which other- 

 wise might have remained latent, grow out 

 into shoots (figs. 873, 1055). Such a re- 

 placement by similar organs of an organ 

 that has been removed, or whose growth 

 has been checked, is known as regeneration. 

 In animals a lost part commonly is regener- 

 ated at the place of severance. This rarely 

 occurs in plants, possibly because of the 

 presence of latent buds. In roots and in 



some leaves (as in Cyclamen), where there are no such latent buds, the 

 lost part may be restored at the cut surface, as in animals (p. 503); 

 the regeneration of a lost part at the cut surface may be termed restitution. 



FIG. 1071. Regeneration 

 in the scarlet runner bean 

 (Phaseolus muUiflorus) ; the 

 epicotyl of a seedling was cut 

 away, whereupon the minute 

 primordia in the axils of the 

 cotyledons developed into 

 vigorous shoots. After 

 McCALLUM (drawn from a 

 photographic reproduction). 



