MECHANICAL ELEMENTS OF PLANTS. 189 



with a length of 300 feet are not uncommon, and some figures 

 much higher than this are noted. 



524. In both the above cases the extraordinary size has been 

 attained with very little expenditure of material for mere me- 

 chanical support. The same is true, although in a less striking 

 because a more familiar manner, in our ordinary twining and 

 climbing plants ; other plants or outside supports of some kind 

 beino- necessary to bring their stems and leaves into the best 

 relations to their surroundings. But what tissues serve to keep 

 erect or in position the larger plants which are not water-plants 

 or climbers? What tissues serve mainly mechanical ends? 



525. The subject w r as extensively investigated, so far as 

 monocotyledonous plants are concerned, by Schwendener, 1 in 

 1874, since which time some important additions have been 

 made. According to Schwendener, the mechanical elements 

 in the plant are (1) bast-fibres, (2) libriform cells and fibres, 

 (3) collenchyma cells. That these are the chief elements of 

 strength, especially in monocot\-ledonous plants, appears from 

 his instructive experiments, which have been repeated by others. 

 Strips, 150 to 400 mm. in length and about 2 to 5 mm. wide, were 

 carefully taken from stems or leaves and immediately fastened 



/ * 



in a vise at one end, the other end being firmly grasped by strong 

 pincers to which weights could be attached at will. Behind a 

 strip, vertically suspended from the vise, a measuring-bar was 

 placed, so that any elongation of the strip under tension could be 

 accurately measured. After the apparatus was properly adjusted, 

 a small weight was attached to the pincers, the elongation of 

 the strip observed, and the weight then removed in order to see 

 whether the strip recovered its original length. Up to a certain 

 point the recoveiy was found to be complete ; beyond this point 

 the elasticity was lost, and not again regained. 



526. Strips from the middle part of the leaf of Phormium 

 tenax, 390 mm. long and 1.5 to 2 mm. wide, were placed in the 

 apparatus and subjected to the action of a weight of 10 kilograms. 

 The}' became 5 mm. longer, but on removal of the weight were 

 found to recover their original length ; in other words, they re- 

 mained perfectly elastic under this weight. A weight of 15 

 kilograms broke the strips into two parts. These strips con- 

 tained only five fibro- vascular bundles, with an amount of bast 

 which was believed to be about half a square millimeter in cross- 



1 Das mechanische Princip im anatomischen Ban der Monocotylen (Leipzig, 

 1874). 



