The Mechanical Structure of Plants. 



BY J. COCHRANE, HAVANA, ILL. 



[C0NTINUED.J 



IN the above enumeration we first notice a unity of purpose under a variety of ex- 

 pedients. Nothing can be more single than the design, more diversified than the 

 means. Pefficles, shells, pulps, pods, husks, skins, scales armed with thorns, are all 

 mechanically emplnyed for the same end. Secondly we may observe, that in all 

 these cases the purpose is fulfilled within a just and limited degree. We can per- 

 ceive that if the seeds of plants were more strongly guarded than they are, their 

 greater security would interfere with other uses, many species of animals would 

 perish if they could not obtain access to them. Here, as in many cases, a balance is 

 to be maintained between opposite uses. The provision for the preservation of seeds, 

 appears to be directed chiefl}' against the inconstancy of the elements, and the 

 inclement season. The depredations of animals and the injuries of accidental 

 violenc*, seem to be provided against by the abundance of the increase, 



Whfen nature has perfected her seeds, her next care is to disperse them. The 

 seed cannot fulfill its ends while it remains in the capsule. After the seed ripens, 

 the pericarpium opens to let them out, which is according to rule in each species of 

 plant. Some are opened by the action of the frost, some by elastic explosion, 

 throwing the seeds to a distance. Those of most composite flowers are endowed 

 with downy appendages, by which they float in the air, and are carried to great 

 distances. We are compelled to omit to notice the store of nutriment laid up in the 

 seed for the nutriment of the young plant. A striking analogy exists between seeds 

 and eggs of animals; the same point is provided for in the same manner. The 

 white, and that only, is used in the formation of the chicken. The yolk, very little 

 altered or diminished, is wrapped up in the abdomen of the young bird, to serve for 

 its nourishment till it has learned to pick its own food. We give the most common 

 as illustrations because of their being the most forcible. 



Our second observation on the mechanical structure of plants, is upon the general 

 property of climbers. In these, plants from each joint issue close to each other, 

 two shoots, one bearing the flower and fruit, and the other drawn out to a tapering 

 spiral tendril, that attaches to anything within its reach, considering that two pur- 

 poses are to be provided, for the fruitage of the plant and the sustentation of the 

 stalk. No means could be more mechanical than this arrangement presents to the 

 eye. •' We do not see," says a noted author, '^ so much as one tree, shrub or herb, 

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