712 NOTES 



matter of fact, be <li<l attempt to define the dermal and vascular systems from that 

 point of view, though perhaps not with complete success. All the remaining tissues, 

 on the other hand, are classed together as '"ground-tissue" or "fundamental 

 tissue," in contradistinction to the dermal tissue and the vascular bundles. But 

 this ground-tissue includes green photosynthetic parenchyma, colourless water- 

 tissue, storage-parenchyma, mechanical strands and cell-masses, endodermal layers 

 and the multifarious tissues which make up pericaps and seed-coats. No one, 

 therefore, will venture to maintain that "ground-tissue" constitutes a 'whole of 

 definite physiological character." 



De Bary (I.e. p. 6) has pointed out that the conception of a " ground-tissue " is 

 inadmissable even from a purely anatomical standpoint. " However much the sub- 

 division of tissues into three main systems may be fitted to guide beginners, still, 

 in my opinion, it does not answer its purpose, which is to serve as a basis for a 

 uniform exposition of the various differentiation of plant-tissues. For the names 

 Dermal and Fascicular [= Vascular] Tissue indicate, in Vascular plants, systems of 

 tissue, which are positively characterised by definite tissue-forms ; but the name 

 Fundamental tissue implies the remainder, and this may just as much consist of 

 different positively characterised tissue forms, and tissue-systems, which are equiva- 

 lent to the Dermal and Fascicular systems." 



In the author's opinion, successful application of the anatomico-physiological 

 classification of tissues will provide a more satisfactory proof of the practical value 

 of this system than any academic discussion cf its merits ; it is hoped that the 

 present work will be found to justify this belief. One point of detail may be specially 

 referred to. Objection is frequently raised to the physiological classification of tissues, 

 on the ground that most tissues perform more than one function, and must conse- 

 quently be referred to one or another physiological tissue-system, according to the 

 function which happens to be under consideration at the moment. But if the dis- 

 tinction between principal and subsidiary functions which is no mere theoretical 

 conception but an actual fact is kept in mind, there should be no difficulty or risk 

 of error in assigning the various tissues to their proper systems. The principal function 

 should be the sole guide in this connection. So far as the Higher Plants (from the 

 Archegoniatae upwards) are concerned, there should rarely be any doubt as to 

 which of the various functions of a tissue is the principal one ; where uncertainty 

 exists, the systematic position of the tissue is indeterminate. It is surely also per- 

 missible to remark, that the purely descriptive anatomists are also sometimes in 

 doubt as to the correct systematic position of individual tissues, and that they have 

 by no means always been in whole-hearted agreement with regard to the anatomical 

 classification of tissues. 



The need for a physiological classification was felt sooner by animal anatomists 

 and histologists, than by botanists. The prominent histologist Leydig, for example, 

 in his Lehrbuch der Histologic des Menschen unci der Thiere (1857), sets up a 

 physiological classification of animal tissues, justifying his action with the following 

 words (I.e. p. 21): "In my opinion, the classification of tissues, more especially, 

 should be carried out without reference, in the first instance, to morphological 

 characteristics. ... My own classification accordingly, is based upon the physiologi- 

 cal relations of the structural elements." Cf. also Hermann v. Meyer : Biol. Centr. 

 1883, No. 12. 



(The above note, which is reproduced almost word for word from the first 

 [German] edition, is included chiefly on account of its historical interest.) 



[31. The term " growing-point " has become so firmly established in English 

 botanical literature, that I decided to retain it here instead of the more accurate 

 " punctum vegetationis."] 



