224 VEGETABLE ORGANOGRAPHY. 



nourishment. These roots arise in preference from 

 knots, tubercles, and in general all parts where there is 

 any deposit of nutritive matter. The art of making 

 them to be produced constitutes the operation of laying, 

 &c. When the adventitious roots arise in the air, they 

 most frequently present themselves under the form of 

 cylindrical filaments, of a silvery white colour, descend- 

 ing vertically towards the ground ; we see this in 

 Ficus elastica, Clusia rosea, Mhizophora, succulent 

 plants, &c. The length of these filaments reaches, in 

 Clusia and Rhizophora, from eighty to one hundred 

 feet. Sometimes they ramify even when they are pro- 

 duced in the air, as for example in Rhus radicans ; this 

 ramification is especially frequent when the roots are 

 produced in wet moss or earth. 



Turpin has observed that adventitious roots do not 

 augment in diameter before they reach the soil ; but, as 

 soon as they begin to absorb nourishment, they give 

 origin to lateral roots, and they themselves grow in 

 a remarkable degree. 



There are some plants in which adventitious roots 

 alone are found ; such are those which undergo, at the 

 period of germination, that kind of destruction of their 

 base which I have spoken of in the preceding section, 

 and whence it results that the true root is not developed, 

 and that the base of the stem, usually buried in the 

 earth, takes the appearance of a root ; this stem shoots 

 out then a multitude of adventitious roots, and it is with 

 these alone that the plant is provided. This phenome- 

 non frequently takes place in the subterranean stems of 

 herbaceous Ferns, and in a great number of Monocotyle- 

 dons, such as Allium senescens, &c. It is found in 

 Dicotyledons — in the Water Lily. 



Leaves are capable of producing adventitious roots, 

 especially along their petioles : this is observed in 



