164 The Anatomy of Plants BOOK n 



who were averse to the unaccustomed use of the micro- 

 scope in this department of Botany, and feared lest they 

 should have to resign their favourite science to their younger 

 initiated colleagues, and it is not to be wondered at that 

 the new method gained a sound footing. On the other 

 hand, it is not unnatural that a number of botanists of the 

 new school expected too much from the anatomical method, 

 and not only looked for a revival of systematic Botany on 

 a surer basis, but also for an entirely new Natural System.' 



While the method no doubt possesses many advantages, 

 it seems clear that it must not be pressed too far. We 

 have seen that a great danger of misinterpretation of 

 relationship of tissues cannot be dissociated from the pro- 

 posals of Haberlandt and Tschirch to adopt a physiological 

 classification of anatomical structures, and we must there- 

 fore scrutinize very carefully suggestions of systematic 

 affinity which rest on adaptive structures. Solereder 

 himself admits as much, for he says, when speaking of 

 anatomical details : 



' These features are not always characteristic of large 

 groups of plants. Secretory cavities or cells, though often 

 constant throughout entire orders, tribes, or at least genera, 

 may occasionally occur in isolated species. A definite type 

 of stomatal apparatus is found without exception through- 

 out the Rubiaceae, but is only present in isolated members 

 of the allied orders Umbelliferae and Caprifoliaceae. One 

 or more exceptions may not rarely be found in an Order, 

 the remaining members of which are distinguished by a 

 special phyletic character, e.g. Drapetes is exceptional 

 among Thymelaeaceae in possessing no intraxylary phloem. 

 Such cases are not capable of explanation, for these excep- 

 tional members have to be included in the Order concerned 

 on account of the rest of their distinctive characters. All 

 these facts indicate that the value of an anatomical character 

 cannot be definitely predicted.' 



Another movement which was gradually increasing in im- 

 portance up to the close of the century was initiated during 



