NOTES 731 



of palisade-cells. Areschoug, in fact, goes so far as to regard the formal ion of palisade- 

 tissue as a device for restricting transpiration. As a matter of tact, the air-spaces 

 between palisade-cells are by no means always narrow crevices; some forms of 

 palisade-tissue are very loosely put together, and contain an exceedingly well- 

 developed ventilating system. Further, Volkens has shown that desert-plants 

 often possess a very loose palisade-tissue, although the structure of their dermal 

 system and stomata shows them to be pronounced xerophytes. It is therefore 

 quite clear that the shape and orientation of palisade-cells have no connection with 

 the intensity of transpiration. In any case, narrow intercellular spaces can be 

 developed quite as readily hi an isodiametric photosynthetic parenchyma as in 

 palisade-tissue ; conversely, enlargement of the ventilating spaces or, in other 

 words, of the transpiring surface can be achieved quite as readily within palisade- 

 parenchyma as in any other form of tissue. 



Warming regards the frequent convergence of groups of palisade- cells towards 

 collecting-cells (cf. p. 285, and Figs 116 and 117), as an adaptation which serves to 

 enlarge the intercellular spaces in proportion to their distance from the upper side 

 of the leaf. This interpretation does not commend itself to the author's judgment. 

 Even if such a progressive enlargement of the intercellular spaces were needed, 

 which remains to be proved it could be equally well achieved by various other 

 modes of arrangement of the palisade-cells. 



153. G. Haberlandt : P.J. 17, 1886. Magdeburg : Die Laubmooskapsel als 

 Assimilationsorgan (Inaug.-Diss.), Berlin, 1886. Roedler : I.e. [146]. 



154. Wille : K. Svenska Handl. 21, 1885. A. Hansen: Mitth. Neapel, 

 2, 1893. 



155. G. Haberlandt : Mitth. Steiermk. 1880. 



156. Pfeffer : Abh. sachs. Ges. 18, 1892. Id. Physiology, 1, pp. 587 sqq., 

 Czapek : Sitzb. Wien, 106, 1897. 



157. Von Mohl : Verm. Schriften, p. 285. Sanio : B.Z. 1868, p. 113. Caspary : 

 Monatsber. Berl. Akad. 1862 (July). De Bary : Comp. Anat. pp. 155 sqq. Stras- 

 burger : tjb. d. Bau. u. d. Verrichtungen d. Leitungsbahnen in d. Pflanzen, Jena, 

 1891, pp. 510 sqq., et passim. The terms " trachea " and " tracheide " were intro- 

 duced at a time when anatomists generally believed, that the structures in question 

 represented ventilating organs analogous to the tracheal tubes of insects. As it 

 is now established, beyond any possibility of doubt, that the tracheae and tracheides 

 of plants are water-conducting tubes, it becomes necessary to consider whether the 

 modification of our views concerning the functions of these structures necessitates 

 any change of terminology. Potonie has, in fact, suggested (Ub. d. Zusammen- 

 setzung d. Leitbundel b. d. Gefasskryptogamen, 1883), that the water-conducting- 

 system as a whole might be termed the ' ! hydrome," and its component elements 

 " hydroids." The aptness of these terms cannot be denied ; but the author has 

 yet to be convinced of the need for a new terminology. Etymologically, the terms 

 " trachea " and " tracheid " are derived from the Greek rpa^vi, signifying rough, 

 hard or uneven, and really imply that the walls of the tubular structures to which 

 they are applied are furnished with devices for increasing their mechanical strength ; 

 as they may therefore be quite properly applied to water-conducting tubes, t lien- 

 is no need to depart from the old-established terminology. 



158. Rothert : Bull. Acad. Crac. IS'.l!). Kornicke : Sitzb. niederrhein. Ges. 

 1899. 



