OBLIQUE PALISADE-TISSUE 291 



not as a rule bear any relation either to translocatory arrangements or 

 to the conditions of illumination. Pick himself, it is true, regards the 

 obliquity which he found to occur especially in vertically-extended 

 photosynthetic organs as an adaptation directly induced by oblique 

 illumination ; but Heinricher has shown that this view cannot possibly 

 be maintained in face of the fact that the degree of obliquity may vary 

 in different parts of the same leaf. In Isolepis australis, for example, the 

 inclination of the palisade-cells to the vertical is 40 beneath the sub- 

 epidermal fibrous strands, but only 14 where the palisade-tissue abuts 

 immediately against the epidermis. The obliquity is also often more 

 pronounced on the lower side of the leaf; in Asperula longiflora, for 

 instance, the corresponding angles are 20 for the lower side, and not more 

 than 5 for the upper. Heinricher has further shown in the case of Isolepis 

 australis (and the author has confirmed his results for certain other 

 plants) that the palisade-cells all slope in the 

 same direction namely, towards the leaf-apex 

 in spite of the fact that only the basal portion 

 of the leaf is erect, while the apical region is 

 reclinate ; as far as the drooping part of the 

 organ is concerned, the orientation of the palisade- 



" ' l Fig. 120. 



cells is obviously incompatible with Pick's , . 



" x Oblique palisade-cells in the 



hypothesis. The author has, moreover, observed young leaf of omithogaium 



. . byzantinum ; the portion 



that the displacement of the palisade-cells may figured is stm beiow ground 



* . L 'at this stage. 



take place while the leaves in question are quite 



young and still enclosed within a bud or buried in the ground {Dactylis 

 glomerata, Poa annua, Omithogaium nutans, Scilla oifolia, Allium asca- 

 lonicum, Narcissus poeticus; cf. Fig. 120); in these circumstances the 

 influence of light is, of course, entirely excluded. Further research 

 is, however, needed, before the origin and significance of this by no 

 means uncommon oblique orientation of the palisade-tissue can be 

 satisfactorily explained. 



2. Experimental Data concerning the Emigration of Carbohydrates 

 from the Photosynthetic System. 1 '* 8 ' 



The author has succeeded in identifying the paths by which the 

 carbohydrate material manufactured in the photosynthetic cells emigrates 

 from the leaves, by the methods of comparative anatomy. In accord- 

 ance with the principle of expeditious translocation, the synthetic 

 products pass, in the case of a typical Dicotyledonous leaf, from the 

 palisade-tissue through the collecting cells into the intermediary tissue 

 or spongy parenchyma, and thence into the parenchymatous bundle- 

 sheaths, or the conducting parenchyma of the principal veins, as the case 

 may^be; the reticulately-disposed conducting parenchyma thus represents 



