1905.] NATURAL SCIENCES OF PHILADELPHIA. 703 



Given alternating periods of dry and wet weather, or given condi- 

 tions which are at seasons prejudicial to the best growth of this palmetto, 

 we would find alternate constrictions and enlargements of the stem in 

 response to the environmental conditions. In seasons favorable to 

 growth, the growing apex of the stem would expand itself with a cor- 

 respondingly larger crown of leaves and increased diameter growth of 

 the stem. During dry periods, the apex would become contracted, the 

 crown of leaves smaller and the stem diameter correspondingly con- 

 stricted, or contracted. The stem diameter is controlled by the size of the 

 crown, and the size of the crown is in direct response to the meteor- 

 ologic, edaphic and physiologic conditions which surround the tree. 

 A comparison of figs. 18 and 12, representing trees growing in wet 

 marshy ground, with figs. 9, 14 and 20, illustrating trees found in 

 dry rocky situations, will show that the statements made above are 

 almost axiomatic. 



That climate influences the cell growth of palms is illustrated by a 

 specimen in the botanical laboratory of the University of Pennsylva- 

 nia, presented by S. L. Schumo. It is a section of stem of a Sabal 

 palmetto which grew at Daytona, Florida. The cross section shows 

 evidence of two rings of growth outside of the main, uniformly-con- 

 structed cylinder of bundles and parenchymatous tissue. The de- 

 scription accompanying the specimen states that the tree from which 

 the section was made shed its leaves in a manner similar to the horse- 

 chestnut, so that the petiole was left attached to the main stem. The 

 statement also is made that the natives claim that the petioles, which 

 they call bootjacks, all fall off and then the trunk becomes bare 

 when this tree becomes mature. It is evident, therefore, that the 

 recm-rent fall of leaves from this tree, just as in typical dicotyledonous 

 stems with concentric annual rings of wood, has produced the corres- 

 ponding stem structure just described — that is the appearance of two 

 well-marked rings, external to the central uniform stem cylinder. 



The secondary growth in thickness which we have described for 

 the Bermuda palmetto, where the stem is alternately enlarged and 

 contracted producing the hour-glass forms, is different from the sec- 

 ondary growth in thickness displayed by Sabal palmetto in Florida. 

 However, the fact that palms do show secondary growth in thickness 

 renders these examples absolutely unique, as far as the information of 

 the writer goes. 



Another fact of somewhat similar import may be mentioned, namely, 

 that the stems of the coconut palm, Cocos nucifera, as seen by the 

 writer in Jamaica, and of the Bermuda palmetto, Sabal Blackburniana, 



