^06 KUiMK.sl^ <>K STRUCTURAL HOTANV. 



356. The Algee, Fungi, and Lichens together constitute 

 a great group called ThallophyteS. The Lichens from 

 their peculiar constitution may be regarded as transitional 

 between the Alga? and the Fungi, and by some the Charas 

 are looked upon as links between the Algse and the 

 Bryophytes. 



Some further reference will be made to the Thallophytes 

 in the next chapter, in which is given a brief outline of 

 the classification of plants generally. 



CHAPTER XXIV. 



CLASSIFICATION OF PLANTS ACCORDING TO THE NATURAL 

 SYSTEM. 



357. Hitherto our examination of plants has been 

 confined to a few selected specimens, and we have 

 examined these chiefly in order to become acquainted 

 with some variations in the details of growth, as exem- 

 plified by them. Thus we have found plants which agree 

 in exhibiting two cotyledons in the embryo, and others, 

 again, which are monocotyledonous. Some members of 

 the former group were found to exhibit two sets of floral 

 envelopes, other only one, and others, again, were entirely 

 without these organs. And so on through the various 

 details. We now set out with the vegetable world before 

 us a world populated by forms almost infinite in number 

 and variety. If, therefore, our study of these forms is 

 to be carried on to advantage, we shall have to resolve 

 upon some definite plan or system upon which to proceed ; 

 otherwise we shall merely dissipate our energies, and our 

 results will be without meaning. Just as, in our study 



