218 Retrograde Varieties 



shape proper to the young trees, bearing sessile 

 and opposite leaves. 



It seerns quite unnecessary to give further 

 instances. They are familiar to every student. 

 It is almost safe to say that every character has 

 its periods of activity and of inactivity, and 

 numbers of flowers and fruits can be mentioned 

 as illustrations. One fact may be added to 

 show that nearly every part of the plant must 

 have the power of producing all or nearly all 

 the characters of the individual to which it 

 belongs. This proof is given by the formation 

 of adventitious buds. These, when once 

 formed, may grow out into twigs, with leaves 

 and flowers and roots. They may even be sep- 

 arated from the plants, and used as cuttings, 

 to reproduce the whole. Hence we may 

 conclude that all tissues, which possess the 

 power of producing adventitious buds, must 

 conceal in a latent state, all the numerous char- 

 acters required for the full development of the 

 whole individual. 



Adventitious buds may proceed from spe- 

 cialized cells, as on the margin of the leaves of 

 Bryophyllum calycinum; or from the cells of 

 special tissues, as in the epidermis of the be- 

 gonias; or they may be provoked by wounds 

 in nearly every part of the plant provided it 

 be able to heal the wound by swelling tissues or 



