32 



MORPHOLOGY OP THE BOOT. 



54. But some plants, such as the Radish, which when they 

 spring from seed in autumn are true biennials, will when raised 

 in spring pass on directly to the flowering stage in summer, or 

 when sown after tlae warm season begins will often run through 

 their course as annuals. Then there are various biennials which 

 thicken the root very little and hold their leaves through the 

 winter. Between these and winter annuals no clear demarcation 

 can be drawn. As respects annual and biennial duration, the 

 terms may for the most part be applied indiscriminately to the 

 plant or to the root. We may say either that the plant is a 

 biennial, or that its root is biennial. 



55. Perennials are plants which live and blossom or fructify 

 year after year. They may or they may not have perennial 



roots. In trees and shrubs, also in 

 herbs with growth from year to year 

 from a strong tap-root, the root 

 is naturally perennial. But in most 

 perennials with only fibrous roots, 

 these are produced anew from time 

 to time or from year to year. Also, 

 while some such roots remain fibrous 

 and serve only for absorption, others 

 may thicken in the manner of the 

 ordinarj- biennial root and serve a 

 similar use, *'. e. become reservoirs of 

 elaborated nourishment. The Dahlia 

 (Fig. G8) and the Peony afford good 

 examples of this. Sweet potato is 

 another instance. 1 Most such roots 

 have only a biennial duration : they 

 are produced in one growing season ; they yield their store to 

 form or aid the growth of the next. When perennials store up 

 nutritive matter underground, the deposit is more commonly 

 made in a subterranean portion of the stem, in tubers, corms, 

 bulbs, &c. (See 115-122.) 



56. The distinction between annuals and biennials is at times 

 so difficult, and the particular in which they agree so manifest, 

 namety, that of blossoming only once, then dying, as it were 

 by exhaustion, that it was proposed by DeCandolle to unite 



1 It is only by the readiness of this root to produce adventitious buds, 

 especially from its upper part, that it has been mistaken for a tuber, such 

 as the common potato. 



FTO. 68. Fnsdcled and tuberous or fusiform (secondary) roots of Dahlia : a, a. buds 

 on base of the stem. 



