318 CONNEXION OF STRUCTURE AND PROPERTIES. 



479. There is a point of agreement among the plants brought 

 together in Natural Orders, which is of the greatest practical 

 importance. This is, that those which agree in structure almost 

 invariably correspond in properties also. For instance, the whole 

 of the Papaveraceae or Poppy tribe possess narcotic properties ; 

 all the Ranunculaceae or Crowfoot tribe are acrid ; whilst all the 

 Malvaceae or Mallow tribe are destitute of unwholesome proper- 

 ties. Thus, when a plant is recognised as a member of a parti- 

 cular Natural Order, an almost certain account may be given of 

 its properties, whether it is likely to be injurious or wholesome, 

 to furnish valuable medicines, or important articles of food. It 

 must be remembered, however, that the peculiar properties of 

 the plant do not pervade every portion of it ; and that it may 

 hence be possible to obtain wholesome nutriment, even from 

 members of orders most distinguished for their deleterious pro- 

 perties. Thus the Potato belongs to the order Solaneae, which 

 contains the Deadly Nightshade, Henbane, and other poisonous 

 plants ; but the edible part of it, which is a deposition of starch 

 for an express purpose (. 337), is free, or nearly so, from the 

 narcotic properties which exist in the stems and leaves. Indeed, 

 as a general rule, such depositions of starch may supply whole- 

 some food in any order, more especially if care be taken to free 

 them from any juices they may contain ; thus the Cassava, which 

 furnishes one of the most important articles of food to the inha- 

 bitants of many tropical countries, is obtained from a plant of 

 the order Euphorbiaeece or Spurge tribe, which is distinguished 

 for its very acrid qualities : and these are principally restricted 

 to the juice expressed from the meal after it has been ground. 



480. The Linnaean system, however, is not without its ad- 

 vantages for particular purposes. To a person commencing by 

 himself the study of Systematic Botany, desirous of making him- 

 self acquainted with the names and characters of the plants he 

 may meet with in his walks, and not ambitious of extending his 

 studies to the higher parts of the science, the Linnaean system, 

 when applied with the aid of books, possesses facilities which are 

 (at present at least) greatly superior to those afforded by the 

 other, and which are well calculated to encourage a learner. To 

 count the number of stamens and pistils is generally a very easy 



