118 RELATIONS OF MAN WITH EXTERNAL NATURE. 



hence the Dicotyledons are also named Exogens ; their leaves present a branched 

 and reticular arrangement of the so-called veins. The Dicotyledons include 

 the great majority of the European flora, comprehending the timber, forest, 

 and fruit trees, shrubs, and most of the firm-stemmed herbaceous plants. 



The Monocotyledona also produce true leaves, flowers, and seeds ; but, as 

 their name implies, the seed has only one seed-lobe or cotyledon, which germinates 

 into a single embryonic leaf. Their whole structure is simpler than that of 

 the Dicotyledona. The vascular and woody tissue of their stems is not de- 

 posited in successive concentric layers ; but is collected into numerous bun- 

 dles, diffused or scattered through all parts of the cellular or pithy structure 

 of the stem ; hence these plants are also named Endogens. Their leaves are 

 characterized by a parallel arrangement of the veins. The Monocotyledons 

 are fewer in number than the Dicotyledons, and are rarer in Europe. Mono- 

 cotyledonous trees, such as the bananas and the palms, are found only in hot 

 countries. Most of these plants are herbaceous, such as the orchids, the irids, 

 amaryllids, and lilies, the asparagus, colchicum, and arum, the sedges and 

 the extensive and varied family of grasses, including the bamboo, sugarcane, 

 rice, maize, wheat, rye, barley, oats, and all the varieties of meadow-grass. 



The Acotyledona, corresponding with the Cryptogamia, produce neither 

 true leaves, flowers, nor seeds, and accordingly, as their name implies, have 

 no seed-lobe or cotyledon. They are reproduced by much more simple struc- 

 tures, viz., single cells, often quite microscopic, named spores. In the larger 

 kinds, a stem is developed, consisting of both vascular and cellular tissue, the 

 former being in that case, either collected into a central mass, or into a few 

 large regularly folded masses ; these are named the vascular Acotyledons ; 

 they possess leaves or leaf-like parts, sometimes named fronds. In other and 

 simpler kinds of Acotyledons, there is no vascular tissue, the entire plant 

 being formed of cells ; hence these are called cellular Acotyledons. The stem 

 of the vascular Acotyledona and of one family of the cellular group, viz., the 

 mosses, grows or increases only at the point or apex ; hence these have been 

 named Acrogens; whilst the remaining cellular forms have 'neither stem, root, 

 nor leaves, but consist of a fused mass of cells, called a tliallus, and hence 

 are named Thallogens. Amongst the vascular Acotyledons are found the 

 lycopodiums, or club-mosses, some of which attain the height of trees ; the 

 ferns, some of which, like the Cycas, also reach a great height and size ; and 

 lastly the equisetums. To the cellular Acotyledons belong the mosses, the 

 enormous family of fungi, including the large boletuses and agarics, the truffles 

 and morells, and all the minute microscopic fungi, such as the Penicillium, 

 Mycetum, Oidium, Botryllus, and others ; also the various lichens, and lastly 

 the algae or confervse, some of which, such as the sea-weeds, are of gigantic 

 dimensions, whilst some, like the Desmideae, Diatomaceae, Oscillatoriae, Vol- 

 vocinae, Protococci, Monadinae, and others, are quite microscopic ; many of 

 these have been, from their manifestation of movement, erroneously classed 

 with the infusorial animalcules. Amongst the fungoid group, the Mycetozoa, 

 and, amongst the confervoid forms, the Vibrionia, occupy a doubtful position 

 between the animal and the vegetable kingdoms. 



Structure and Functions of Plants. Plants, like animals, have a definite 

 organization and structure, and arc endowed with special functions and prop- 

 erties, which are the subjects of study in vegetable anatomy and physiology. 

 The characteristic functions of plants are those of nutrition and reproduction ; 

 for in the few instances, to be hereafter mentioned, in which partial or general 

 movements occur in them, such movements are involuntary and, when their 

 purpose is evident, concur in one or other of the two proper vegetative func- 

 tions. The chief nutritive organs in Exogens, Endogens, and Acrogens, are 

 the roots, with their soft terminal absorbing points named spongioles, the stem, 

 and its branches, and the leaves or leafy fronds. The roots, the proper organs 

 of absorption, take up water holding in solution carbonic acid, ammonia, sul- 

 phates, phosphates, and other saline materials, constituting the ultimate food 

 of plants. The stem and branches convey these materials, now somewhat 

 enriched by substances already contained in the plant, upwards to all parts, 

 in the form of the ascending sap. The leaves are the seats of the active elabo- 

 rative vito-chemical processes of the plant : it is from their surface that the 



