194- TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



strict accordance with mechanical principles. Tha 

 strength of a hollow cylinder is greatly augmented 

 by thickened bands passing round it at intervals, as 

 these prevent the collapse of the cylinder on the 

 side where the greatest strain hai)pens to fall. The 

 knotted stems of the bamboo and other grasses, of 

 pinks, geraniums, &c., afPord interesting illustrations 

 of this. In many grasses no two internodes are 

 exactly in the same straight line. The adjacent 

 internodes are observed to form an obtuse angle 

 with each other at the joint. The effect of this 

 arrangement is rather curious. When a gust bends the 

 stem, the result is not that the stem simply vibrates 

 in one plane, but the linear motion produced by the 

 wind is resolved, as if by a crank, into a circular 

 movement of circumnutation. This is doubtless of 

 service in promoting symmetrical growth by draw- 

 ing the saiD up every side of the stem. The power 

 which grasses have of recovering their vertical posi- 

 tion if thrown down, by grov/th taking place on 

 one side of a node, is also of great importance. 

 The amount of silica deposited in the cells of the 

 stem doubtless also contributes to their strength. 



Climbrng stems have been studied chiefly in rela- 

 tion to light. One great advantage, which climbing 

 plants possess over others, is, no doubt, tliat by 

 this habit they are enabled to get their leaves more 

 quickly up to the light. In a thick Avood this must 

 be of the highest importance. At the same time 

 climbers avoid the exj)enditure of material necessary 

 to form an erect, woody, self-supporting stem. The 

 climbing habit, however, is also advantageous, as 

 enabling a plant to contend with the wind, and may 

 in some cases have been acquired for this reason. 

 The large leaves of some climbers would lead us 

 to think that the advantage of climbing was qviite 

 as great in relation to the destructive force of wind 

 as it is in enabling the plant to gain access to the 

 light. 



If we are not yet in a position to form very 



