304 PHYSIOLOGICAL BOTANY. PART II. 



under the influence of the moisture and shade which 

 prevail there. 



(311.) Means of Transport. 



1 . Currents. Rivers and other currents of fresh 

 water are among the most effectual means of dispersing 

 the seeds of plants: even the sea may occasionally 

 serve a like purpose where the seed is protected from 

 its influence by some accidental circumstance. 



2. Atmosphere. Many seeds are provided with 

 downy and winglike appendages, by which their dis- 

 persion is secured ; but more especially the minute im- 

 palpable sporules of cryptogamic plants appear capable 

 of being wafted to very considerable distances by this 

 means. It has been supposed that two species of lichen 

 found on the coasts of Bretagne, have been brought 

 thither from Jamaica by the prevalence of the south- 

 west winds. 



3. Animals. Seeds often become entangled in the 

 hair and wool of many animals, and may thus be carried 

 by them to considerable distances from the spot where 

 they grew ; but more especially such as are furnished 

 witli hard pericarps, or bony coverings to the kernel 

 (as in stone-fruits) are capable of resisting the digestive 1 

 powers of the stomach, and are thus conveyed by birds 

 from one region to another in a state fitted for germin- 

 ation. But man is most instrumental in the disper- 

 sion of different kinds of plants. The seeds of some 

 he has carried intentionally from one quarter of the 

 globe to another ; and others have been accidentally 

 transported by him in a thousand ways, and follow 

 his footsteps wherever he has penetrated. 



(312.) Botanical Rpyirmf*. It seems to tea natural 

 consequence of our considering the geographical distri- 

 bution of every species to have taken place by its gradual 

 dispersion from one definite spot on the earth's surface, 

 that some would be found only in one district, and 

 others in another, provided these were separated by 

 some great physical feature, such as a chain of moun- 

 tains or a wide sea ; and that two such districts, though 



