LECT. IV.] THE ROOT. 127 



much as many succulent plants in arid situations 

 do not receive their nutriment by the root ; nor is 

 the root the nutritious organ in the tribes named 

 Hepaticee *, Confervse *j~, and Fuci ; in all of 

 which it can be regarded as an attaching organ 

 only, designed to secure the individual to the soil, 

 or to the substance on which it is fixed. A less 

 exceptionable definition is that adopted by Mr. 

 Keith, which characterizes the root as " that part 

 " of the plant by which it attaches itself to the soil 

 " in which it grows, or to the substance on which 

 " it feeds, and is the principal organ of nutrition ||." 

 It might be stated, as an objection to this defini- 

 tion, that plants exist which have roots, and, yet, 

 are not fixed by them either to the soil or to 

 any other substance ; as for example, Duckweed 

 (Lemna), a small green lenticular plant, which 

 floats abundantly on the surface of our stagnant 

 pools in summer, and has unattached roots which 

 hang perpendicularly loose in the water. But all 

 plants are at first attached ; and as it is impossible 

 to frame any definition to which no exception 



* A tribe of small herbaceous plants resembling the Mosses 

 found in damp shacfed places. 



(- An aquatic genus, consisting of fibrous, or threadlike 

 jointed and branched parts, closely matted together. 



Marine plants of various forms attached to rocks and 

 stones. 



|| System of physiological Botany, vol. i. p. 33. 



