66 SOUTH AFRICAN FLOWERING PLANTS, 



How readily a species will change is often well 

 seen under cultivation. Thus there are two species of 

 Ar'abis (Cruciferce) in Switzerland, one of which lives 

 in crannies of rocks, and has thin " papery " leaves, and 

 is called A. anchoret' ica ; the other has thicker leaves, and 

 is known as A. al^n'na. When, however, the former 

 was grown in the public gardens at Kew, it assumed 

 all the features of the latter. As another example, 

 there is a spiny plant known as " Kest-harrow " in 

 England, common in dry, waste places, called Ono'nis 

 s'pino'sa ; but plants raised from seed in a border kept 

 constantly moist ceased to produce spines, and assumed 

 the characters of the spineless species, 0, re'pens. 



Plants by the seaside often have somewhat fleshy 

 leaves ; but if they be grown far away inland, they will 

 sometimes produce thin leaves like other plants of the 

 same neighbourhood; and if garden- cress, etc., be watered 

 with salt and water, their leaves then become fleshy, 

 resembling maritime plants. 



Many other such illustrations could be given ; but 

 these will be sufficient for the reader to understand 

 that new varieties and species come into existence by 

 the power of adaptation w^hich the living protoplasm ^ 

 of plants possess, in response to the direct action of the 

 external conditions of life. 



It is in consequence of this that all water plants of 



1 Tills is the name given to the living substance of animals and 

 plants. 



