9 



plants of 'wlia^ever kind are made up of cells smik as 

 ttose just described, and many have no other structure. In the so- 

 ealled higher plants, however, we meet; with tutes and vessels of 

 various kinds and shapes differently arranged.. Spme of these tubes 

 contain woody deposits, as in those whicli constitute the wood, or the 

 Lard shell of stone fruits j others contain a fiixe ttread or threads 

 coiled up in a spiral manner. A spiral isessel is one which contains 

 one or more such threads rolled up within it. Such vessels are found 

 almost exclusively, in flowering plants, and constitute, therefore, one 

 of the marks of distinction between them and flowerless plants. By 

 bxeaking;across the leaf stalk of a Strawberry, the fine spiral threads 

 may be drawn out and rendered visible to the naked eye. These 

 tubes and vessels are eitber elongated cells, or consist ,pf cells placed 

 pne over another, the intervening partitions being obliterated. All 

 begin existence as globi|.lar cells, and become modified in course of 

 growth. Amass of cells constitutes what is called tissue — cellular 

 tissue; a, mass of vessels constitute nflifiCKZfltr ^jssMe. If the ceills con- 

 tain much woody deposit, we speak of the resulting tissue as iooody. 

 Most plants, moreover, are invested by a skin or bark of some kind. 

 In its simplest and most common condition this consists of one or 

 more layers of flattened cells. Such layers constitute the epidermis, 

 or skin. 



" The plant, in the majority of cases, is rooted in the earth. In 

 other instances it floats in or on the surface of water ; its leaves are 

 exposed to tie atmosphere and to the action of light. Unlike an 

 inirhal, a pltot has no separate mouth and Stomach ; its skin presents 

 an unbroken surface, or at least exhibits, under natural conditions, 

 no apeiture thfough which solid material, however fine, can enter. Its 

 cells and vessels are closed on all sides, as a;rule,and have not, except in rare 

 instanced, aiy direct or immediate , communication one with another. 

 In a,nimals there is a continnous alimentary or food-channel from the 

 iflduth to the stomach and intestines. There is also a series of con- 

 tinuous branching tubes devoted to the circulation of the blood, 

 d:nother set of tubefe destined for the passage of air into and out of the 

 lungs, and so forth. In plants there i^ no such series of directly con- 

 tinuous tubes permeating the whole organism. Erom these facts it 

 iBay readily be inferred that no solid substance can enter into or be 

 digested in them. The plant, then, does not live on solid food, but on 

 that which is liquid or gaseous. 



" We have now to see whence it Obtains its supplies' of such 

 nutriment. Eo'oted in the ground, it has, as a whole, no power of 

 locpmbtion. But thougti this is true of the plant as a whole, it dops 

 not apply to the parts of which it is composed. The roots, for 

 instance, grow and extend themselves, and they grow most freely ift 

 thait direction where food is inost abundant or easily got at. Let one 

 examine the roots of a tree gro:wing on the banks of a stream, and see 

 vyhat a leash of fine rbot-thteacts are produced if the main roots happen 

 to be immersed in the water. In like manner the groviftW and 

 lengthening of the shoots, and the swaying to and fro of the branches, 

 bring the leaves into contact with gaseous food, and enable them to 

 avaiil themselves of it without necessitating the movement of the whole 

 plant from place to place in search of nourishment, as is imperative in 

 the case of most animals. 



