DISSEMINATION OF SEEDS. 61 



must be obtained from without. Different degrees of heat are required by dif- 

 ferent plants, but a temperature from 50° to 80° is most favorable to those of the 

 temperate zones. Such is the genial wannth supplied by the sun. 



b. Water is also requisite for softening the integuments, and for dissolving the 

 dry nutriment stored up in the albumen, or the cotyledons. This is supplied in 

 showers of rain and dew. 



c. Oxygen is requisite, as seen above, for the conversion of starch into sugar ; 

 a process always depending upon the formation and evolution of carbonic acid, a*i 

 well in the seed as in the laboratory of the chemist Tliis is supplied by the 

 water and by the air. 



d. And, finally, darkness is favorable, because it is tlu-ough the influence of 

 light, as will hereafter be shown, that plants absorb carbonic acid from the air, 

 decompose it, retain the carbonic acid, and give back the oxygen only. Light 

 would therefore tend to increase the quantity of carbon, ratlier than diminish it. 

 Hence the seed should be buj-ied in the soil. 



134. The ripened seeds of most plants have the power of retaining their vitality 

 for many years, if they are placed in circumstances wliieh will neither cause them 

 to germinate nor decay, such as a low or moderate temperature, with the absence 

 of moisture. Thus the seeds of maize have been known to grow when 30 years 

 old, rye 40 years, kidney beans 100 years, and the raspbeny and beach plum afcer 

 many centuries.* 



ii. THE DISSEMINATION OF SEEDS 



135. Is a subject highly curious and interesting ; and when attentively consid- 

 ered, sen-es, hke a thousand other cases in the works of Nature, to illustrate the 

 wisdom and design of its great Author. By means of the coma, or pappu?, 

 already described, the seeds of the thistle, dandelion, and numerous other plants, 

 are wafted by winds to considerable ctistances, across rivers, mountains, and even 

 the ocean itself. The Erigcron Canadense, a weed now common on both sides the 

 Atlantic,^ was supposed by Linnaeus to have been transported to Europe from 

 Canada, of which country it is native. 



a. Seeds are also furnished with wings for the same purpose. Others are pro- 

 vided with hooks, or beards, by which they lay hold of men or animals, and arc 

 thus scattered far and wide. 



b. Some seeds, as the Impatiens, which are destitute of all such appendages, are 

 thi-own to some distance by the bursting of the elastic pericarp. Kivers, sti-eams, 

 and the currents of the ocean, are all means of transporting seeds from country to 



* No instance of the longevity of seeds is more remarkable than that rflated by Dr. 

 Lintlley. 'I have before me,' says he, ' three plants of ra.spberries, raised from seeds which 

 were taken from the stomach of a man wliose skeleton was found .30 feet below the surface 

 of the eanh. He had been buried with some coins of the emperor Hadrian, and it is therefore 

 probable that the seeds were 1600 or 1700 years old.' 



Several years ago, in the State of Maine, about 40 miles from the sea, some men, m dig- 

 ging a well, threw up some sand from a remarkable layer, about 20 feet below the surface, 

 and placed it by itself. A year or two afterwards several shrubs sprung up from this sand, 

 grew, produced fruit, and proved to be the beach-plum. 



6 



