238 STRUCTURE AND VITAL PROCESSES OF PLANTS 



(page 45). To a certain degree every plant is enabled to protect 

 itself against the destructive stress of the wind: by means of 

 their petioles they place their many leaves in any direction the 

 wind blows, and thus escape most of the wind-pressure; long 

 linear leaves, as those of the Grass family, wave like a Hag in 

 the wind without opposing it; large leaves as those of the 

 Cocoanut tree are slit into numerous segments to allow the wind 

 to pass through ; the Plantain allows the wind to tear its broad 

 blade into many pieces for the same purpose. In spite of all 

 such means there remains a great deal of pressure to which a 

 stem is subjected, and it follows that, to bear up against this pres- 

 sure, it must be specially strengthened. How much the strength 

 of a stem is strained, can be seen in the culm of a Rice plant, which, 

 with a diameter of five millimetres at its base, growls to a length 

 of one thousand five hundred millimetres; it is indeed marvell- 

 ous to see that this slender stem W'ith its heavy load of leaves 

 and grains is not broken when the wind blows at it. What, 

 then, makes the stem of this or any other plant strong enough 

 to hold its own against the weight of the whole plant wdiich 

 presses it downward, against the bending stress of the wind, which 

 tends to break it, and against the pulling power of the wind 

 which tends to uproot the plant? 



First of all, it is the thick-walled woody cells which not only 

 make up the greater part of the trunk of a tree, but are also 

 present in the annual stems of many herbs. Of equal importance 

 to the strength of the stem are the bast-cells, commonly known 

 as fibres, which are to be found in the inner bark of the stems 

 of dicotyledons (see Flax, page 20) as well as in the fibrous 

 bundles of monocotyledons (p. 138). The strength with which the 

 fibres of plants in general resist any pull is equal to that of the 

 best wroiight-iron and, in certain plants, even exceeds that of 

 steel. 



The arrangement of these cells in the stem is something that 

 makes every student of liotany marvel at the wisdom displayed 

 in the works of nature. The principles of architecture, which man 

 took many centuries to discover, after many trials, are here ex- 

 hibited in their simple original beauty. In the description of the 



