206 ELEMENTS OP STRUCTURAL BOTANY. 



356. The Algse, Fungi, and Lichens together consti- 

 tute a great group called Thallophytes. The Lichens 

 from their peculiar constitution were once regarded as 

 transitional between the Algte and the Fungi, and by- 

 some the Charas are looked upon as links between the 

 Algiie and the Bryophytes. 



Some further reference will be made to the Thallo- 

 phytes 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 

 wfth 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 f oilier group.were found to exhibit two sets of floral 

 envelopes, others 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 I'esolve 

 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 



