104 



ANALYTICAL CLASS-BOOK OF BOTANY. 



All growth takes place between the bark anil wood, by 

 the addition of layers to each. In herbaceous species, 

 though the wood is absent, the distinction between tin- 

 bark ainl pith still remains. The leaves, when present, 

 are di.ttinguUhcd by their branching veins, and are hence 

 called net, or feather-veined leaves. Their seeds have 

 always two opposite cotyledons, except iu the Pine 

 family, which have several. The parts of their flowers 

 are not usually multiples of three, but of some other 

 number. When they have two series of floral envelopes, 

 the calyx and corolla are usually distinguished by differ- 

 ences of color and appearance. 



Endogcns, on the contrary, possess a stem not distin- 

 guishable into bark, wood, and pith, but their structure 

 is homogeneous. The woody stems of this class are 

 composed of bundles of woody fibre disposed without 

 order. The stem is surrounded by an integument which 

 does not increase by layers, like bark. All additions to 

 the woody structure take place in the inside. The her- 

 baceous stems of this class consist chiefly of cellular tis- 

 sue, surrounded by a mere cuticle. The leaves also 

 usually present a remarkable difference from those of 

 Exogeus in their parallel veins, which run the whole 

 length of the leaf unbroken. A few Endogens, however, 

 have net-veined leaves. The flowers usually have their 

 iu threes, or multiples of three. The floral enve- 

 lopes also arc rarely distinguishable into cah x and corolla. 

 The seeds are distinguished by having but one cotyledon, 

 or sometimes two, which arc alternate. 



Such are the principal technical distinctions between 

 these two classes ; but even the herbaceous species pre- 

 sent a remarkable difference in their general appearance, 

 which will soon become a sufficient guide to the student, 

 in nearly all cases. The Lily and Orchis tribes, and- the 

 Grasses, are our best examples of Endogens, as the 

 Palms, and other arborescent species, are confined to 

 tropical countries. All our forest trcos, our shrubs, and 

 the great majority of our most common herbaceous 

 plants, such as the Pea and Bean tribe, and the Umbel- 

 liferous family, arc examples of Exogcns. 



Exogens arc again divided into two sub -classes 

 AXGIOKPEKMS (covered seeds), and UYMXOSPEKMS (naked 

 seeds), on account of some important differences in their 

 reproductive organs, which, in the latter, make a di.-tant 

 approach to the simplicity of the Ferns and Club-mosses. 

 In these plants the staminate flowers arc reduced to 

 mere clusters of stamens, while the ovules, instead of 

 being included in a regular ovary, are borne on the open 

 surface or margin of a carpellary leaf, which takes the 

 place of a pistil, and in the Pine family becomes a har- 



dened scale. This sub-class includes only the Cone- 

 bearing trees, and a small tropical family. The other 

 division, Angiosperms, which have regular pistils with 

 the ovules contained in a proper ovary, comprehends the 

 rest of the Exogcns. 



This sub-class which still includes the great majority 

 of flowering plants, on account of its size, is broken up, 

 for the sake of greater convenience, into three nearly arti- 

 ficial sections. 



Those of polypetalous corollas, form the section 

 POLYPETAL.E ; those with monopetalous corollas are in- 

 cluded under MONOPETAUE, while those destitute of a 

 corolla constitute the section APETAL.E. As these, how- 

 ever, are artificial distinctions, there are in each section 

 plants, which, so far as the corqlla is concerned, would 

 belong to other sections, but whose affinities compel us 

 to place them where they are. 



I Living now considered the principal divisions of 

 Flowering plants, those of Flowerless plants next claim 

 our attention. Cryptogamous plants are divided into 

 three great classes Acrogens, Anophytes, and Thallo- 

 phytcs, depending upon distinctions in the mode of 

 growth. 



THE ACROGENS are those which have a regular axis 

 of growth, like flowering plants. They have also the dis- 

 tinctions of stem, root, and foliage. Their stems consist 

 of woody fibre and ducts, mingled with cellular tis-uc. 

 In their general structure, they are not much inferior to 

 many Phacuogamous plants, except iu their reproductive 

 organs. Their sporangia, or spore-cases, and their 

 spores, bear but a very distant resemblance to the flowers 

 and seeds of Flowering plants. They are called Acito- 

 OEXS (plants growing at top), because the axis grows 

 only at the summit, and never increases in diameter. To 

 this class belong the Scouring Rushes, Club-i 

 Ferns. 



THE Axoi-iiYTEs (;</</ /i/s ijruu-iiuj tipu-nnh), gene- 

 rally preserve the distinctions of root, stem, and leaves; 

 and their reproductive apparatus still bears a remote re- 

 semblance to that of flowering plants. The stem grows 

 upwards, and the root downwards; but their whole 

 structure is composed solely of cellular tissue, except in 

 a \erv few species which have ducts, and hence they are 

 restricted to very low and humble forms, never exceeding 

 a few inches in height. The Mosses and Liverworts are 

 the chief examples of this class. 



Hut when we reach THALLOPHYTES, all distinction 

 between root, stem, and leaves, ceases ; there is no longer 

 any axis of growth, nor are there any organs correspond- 

 ing to the reproductive apparatus of higher types. Them 



