Mechanical tissue development in certain North American vines* 
Howarp H. M. BOWMAN 
During the year 1912, a study was made of various woody vines 
growing in temperate North America, with the idea that there 
might be some relation between them and intermediate forms 
bearing on the origin of the liana habit in these temperate regions. 
This paper refers more particularly to the mechanical tissues of 
these plants. 
The liana habit of course shows no phylogenetic connections and 
in this respect is analogous to parasitism, saprophytism, etc. 
The habit evidently did not arise early in the temperate zone 
since among the plants indigenous to this zone it is developed to a 
very slight extent among the lower orders, Liliales perhaps being 
one of the first, that is, on the arbitrary basis of the codrdination 
of structure with time of origin. In the tropics, however, the 
monocotyledonous families having the liana habit are much more 
numerous, e. g., some bamboos and various members of the 
Palmaceae, Pandanaceae, and Araceae, etc. But if, as some 
recent investigators (see Henslow, 5) conclude, the monocotyls 
arose from the dicotyls, this theory of chronological origin may be 
discredited altogether. At any rate, it is fair to suppose that the 
abit did not arise until there was such dense vegetation as to 
make the habit an advantage to the plant. Most of the lianas, 
according to Schenck’s estimate (see Schimper, 7, p. 197) ten 
elevenths, are tropical because the conditions in the tropical rain 
forests are the causative factors, i. e., deficiency of light and 
abundance of moisture. 
However, the simplest internal physiological reason for the 
Origin of this vine habit seems to be the lack of adequate mechanical 
tissues. A secondary factor is the lengthening of the internodes 
but this. is due to the evident physiological process of elongation 
by diffuse light reaction. This can easily be accounted for by an 
* Contribution from the Wolff Biological Laboratory, Franklin and Marshall 
College, Lancaster, Pennsylvania. 
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