290 The Rev. P. Keith on the Internal Structure of Plants. 



transparent membrane or pellicle, fine as the film of a single 

 epidermis, in which the eye, aided by the assistance even of 

 the best glasses, can discover no traces whatever of organiza- 

 tion ; or if any further analysis is practicable, it is that only 

 which conducts us to the molecules of modern philosophers. 



In the course of the foregoing investigations we have seen 

 the great variety of modes in which the elementary organs are 

 grouped, so as to constitute a class, or order, or division. 

 We have seen that these groupings are constant in the orders 

 or divisions in which they are found, and that the greater the 

 complexity of organization, the higher the rank of the plant, 

 as ascending from the lowly Flag or Fungus, to the tall and 

 spreading tree. It is upon this ground that we have instituted 

 our general distribution of plants into Perfect and Imperfect, 

 with the various intermediate gradations which they exhibit ; 

 and if the two classes are compared together, the superiority 

 of the former will be rendered manifest, whether we regard 

 their external fabric or their internal structure. Perfect 

 plants are furnished with roots, by which they fix themselves 

 firmly to a spot and absorb nourishment from the soil. Many 

 of the imperfect plants are altogether rootless, and live only 

 by imbibition from the atmosphere, or they are apparently a 

 mere root, and are lodged wholly in the earth. Perfect plants 

 are furnished with a stem and branches, giving them elevation, 

 and expansion, and magnitude. Many of the imperfect plants 

 are altogether stemless, and are scarcely elevated above the 

 level of the soil on which they grow. Perfect plants are fur- 

 nished with leaves and conspicuous flowers, as well as with 

 conspicuous fruit, giving verdure and odour and beauty to the 

 forest and to the plain, and filling the land with plenty. Many 

 of the imperfect plants are destitute of leaves entirely, and al- 

 most all of them are destitute of conspicuous flowers as well 

 as of conspicuous fruit, presenting to the beholder nothing 

 that is showy, nothing that is attractive, nothing that is cal- 

 culated to delight the eye. Such are the distinctions arising 

 from the external structure of plants. Their anatomy gives a 

 similar result. In the highest orders of vegetables you have 

 the greatest complexity of internal structure, the vascular and 

 the cellular forms being united, and the caudex composed of 

 epidermis, bark, wood and pith, exhibiting an intricate plexus 

 of concentric and divergent layers, cortical as well as ligneous. 

 In the secondary orders you have less complexity of structure, 

 the vascular and the cellular forms being indeed united, and 

 the caudex composed of epidermis, pulp, and interspersed 

 fibre, but exhibiting no plexus of concentric or divergent 

 layers, whether cortical or ligneous. In the lowest orders 



