DISSEMINATION OF SEEDS. 61 
must be obtained from without. Diiferent 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 warmth 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, as 
well in the seed as in the laboratory of the chemist. This is supplied by the 
water and by the air. 
d. And, finally, darkness is favorable, because it is through the influence of 
light, as will hereafter be shown, that plants absorb carbonic acid from the air, 
decompose it, retain the carbon itself, and give back the oxygen only. Light 
would therefore tend to increase the quantity of carbon, rather than diminish it. 
Hence the seed should be buried 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 which 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 raspberry and beach plum after 
many centuries.* 
§4. THE DISSEMINATION OF SEEDS 
135. Is a subject highly curious and interesting; and when attentively consid- 
ered, serves, like 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 pappus, 
already described, the seeds of the thistle, dandelion, and numerous other plants, 
are wafted by winds to considerable distances, across rivers, mountains, and even 
the ocean itself. The Erigeron 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 are 
thus scattered far and wide. 
b. Some seeds, as the Impatiens, which are destitute of all such appendages, are 
thrown to some distance by the bursting of the elastic pericarp. Rivers, streams, 
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 related by Dr. 
Lindley. ‘I have before me,’ says he, ‘three plants of raspberries, raised from seeds which 
were taken from the stomach of a man whose skeleton was found 30 feet below the surface 
ofthe earth. 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, in 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 afierwards several shrubs sprung up from this sand, 
grew, produced fruit, and proved to be the beach-plum. 
* 
