372 



Plant Physiology 



thenocarpy among grapes. The small seedless black or 

 currant grapes of Greece and the eastern Mediterranean 



region furnish the dried cur- 

 rants of commerce. Other in- 

 stances are to be found in the 

 famous Sultana and a few other 

 raisins now propagated in Cali- 

 fornia as well as in the Medi- 

 terranean region. The percent- 

 age of seedlessness in one of 



FIG. 106. Seedless navel (par- 



thenocarpic) and common the table grapes, Black Eagle, 

 (seed-bearing) orange. j s likewise considerable. The 



cause of seedlessness, or lack of fertilization, in these 

 cases does not seem to have received scientific attention. 



Many varieties of the banana fail to set seed, although 

 it would seem that effective pollen is produced. 



220. Nonsexual reproduction. - - Multiplication by 

 vegetative parts is notably common among plants, wild 

 and cultivated. A single individual may in various ways 

 give rise to a colony or complete plantation of its own kind 

 without the production of seed. These may remain in 

 organic connection for a period of time, or they may be 

 promptly separated, one from another, by the death of 

 connecting parts. Wheat and other cereals and grasses 

 have the habit of stooling; that is, of multiplying by buds 

 from the lower submerged nodes. Blue-grass and John- 

 son-grass are among those plants which produce under- 

 ground stems, while the decumbent Bermuda and quack- 

 grasses are among those which regularly take root at the 

 joints. White-clover spreads in a way analogous to the 

 latter, and the strawberry develops runners which bud 



