1897.] NATURAL SCIENCES OF PHILADELPHIA. 199 



vigorously, the Avhole system of buds above, arrested in its growth 

 by some varying of rhythmic action, is pushed aside to the "extra- 

 axillary " position. 



The character of rhythmic growth-waves has not yet received 

 much attention from vegetable biologists. We know that in the 

 growth of some plants the wave progression seems regular and con- 

 tinuous, and then the form of inflorescence we term centrifugal 

 results ; at other times the rest seems but partial and is resumed 

 retro- actively, presenting to us the centripetal condition. Though 

 ignorant of the manner in which these varying phases of rhythmic 

 growth is brought about, there is no question about the fact. The 

 production of the supra-axillary bud into a spine in GlediUclda is, 

 therefore, easily explainable. Assuming, as has been done in this 

 paper, that an axillary bud is the termination of a growth-wave, 

 and that the growth which has succeeded in establishing itself as 

 leader pushed the bud — the arrested terminal branch — aside ; a lower 

 bud on the arrested branch in the more active line of the subsiding 

 growth-wave, would push into activity sufficiently to become a spine, 

 while all the upper portion of the terminal axis remains for a bud, 

 or, perhaps, a mere " gland." In this case the spine represents a 

 centrifugal growth. But when what appears to us to be a lower 

 bud, but which under the conception here adopted would be an up- 

 per one, first pushes, we may regard it as an illustration of centri- 

 fugal growth in the bud state. 



I may be pardoned for observing with some pride, while making 

 a contribution to the knowledge of other hitherto obscure phases in 

 plant life, that the deductions made in my Salem paper of twenty- 

 four years ago have been fully confirmed. 



NUTRITION AS AFFECTING THE FORMS OF PLANTS AND THEIR 



FLORAL ORGANS. 



It is remarkable that while American students of plant life are 

 leaning more and more toward the belief that variation in plant 

 structure is due to varying degrees of life energy, European botan- 

 ists seem more inclined to search for external conditions as the great 

 factor in these modifications. That internal energy must be in- 

 fluenced to some extent by external conditions is manifest to every 

 observer, but changes brought about by these outside influences are 

 rarely permanent. Efforts have been made to show that acquired 

 characters have become hereditary ; but in most of the instances ad- 



