292 GERMINATION REQUISITES FOR IT. 



607. Wind, water, animals, and man, are instrumental in the dis- 

 semination of seeds. Some seeds, as those of Mahogany, Bignonia, 

 Tecoma, Pine, Asclepias, Epilobium, and the Cotton plant, have winged 

 or feathery appendages, by means of which they are wafted to a dis- 

 tance. The same thing occurs in some indehiscent seed-vessels, as 

 the samara of the Sycamore and Ash, and the achaenia of Dandelion, 

 Thistles, &c. Moisture, as well as dryness, operates in the bursting of 

 seed-vessels. The pod of the Anastatica, or Rose of Jericho, and the 

 capsule of some Mesembryanthemums, exhibit the effects of moisture 

 in a remarkable degree. Animals, by feeding on fleshy fruits, the 

 kernels of which resist the action of the juice of the stomach, dis- 

 seminate seeds ; and man has been the means of transporting seeds 

 from one country to another. In some cases, the pericarps ripen their 

 seeds under ground, and are called hypocarpogean (Wo, under, xm^o;, 

 fruit, and yia,, earth). This is seen in the Arachis hypogaea, or 

 Ground-nut. Others, as Vicia amphicarpos, have both aerial and 

 subterranean fruit. Many seeds are used for food by animals, and a 

 great destruction of them takes place from decay ; but this is compen- 

 sated for by the vast number produced, so as to secure the continuance 

 of the species. The quantity of seeds produced by many plants is 

 very great. In single capsules of Poppy and Tobacco, upwards of 

 40,000 have been counted. 



608. Germination. The act by which the embryo of a seed leaves 

 its state of torpidity, and becomes developed as a new plant, is called 

 germination (germmatio, springing). In order that this process may go 

 on, a certain combination of circumstances is necessary. The chiei 

 requisites are moisture, air, and a certain temperature. Exclusion 

 from light is also beneficial. 



609. Moisture is necessary in order that the nutritive matters may 

 be taken up in a state of solution, and that certain changes may take 

 place in the seed. Dry seeds will not germinate. The quantity of 

 water absorbed by seeds is often very large. Decandolle found that 

 a French bean, weighing 544 milligrammes, absorbed 756 of water. 

 The swelling of Pease by absorption of water is familiar to all. The 

 kernels or seeds by this means are enabled to burst their stony coverings. 



610. The temperature required for germination varies in different 

 seeds. Some demand a tropical heat, others are satisfied with the 

 warmth of our spring. In general, the requisite temperature may be 

 said to vary from 60 to 80 F. Some seeds can bear a temperature 

 which would kill others. Some have been known to germinate after 

 exposure for a short time to the heat of boiling syrup ; others after 

 exposure to a cold of 39 F. Many plants grow in the immediate 

 vicinity of very hot springs, others in cold regions. Edwards and 

 Colin, from their experiments, were led to fix 95 F. as the highest 

 limit of prolonged temperature which cereal grains can bear in water; 



