1883.] development of the Leaves of Pinus Silvestris L. 355 



first are formed by a very definite act of cell-division, the latter 

 merely as the result of unequal growth ; and, though the fact 

 that the chlorophyll corpuscles are closely applied to both is 

 undoubted, yet this feature is probably rather a secondary adapta- 

 tion to environment determined by the presence of the folds, and 

 not the main moving cause in their production, for if it were we 

 should expect them to be constant, and not as they are, very 

 limited in their occurrence. The idea that these pseudo-ingrowths 

 serve as air channels to facilitate the transpiration of watery va- 

 pour as well as affording an increase of surface, is I think from the 

 facts of development very much more probable than Haberlandt 

 seems to regard it, since I have invariably found them in Pinus 

 and in every other case I have examined, even in Trollius europceus, 

 at least at their first origin, to exhibit a small air-space. In con- 

 nection moreover with the recent researches of Boussingault on the 

 absorption and metabolism of Carbon Dioxide gas by leaves they 

 would also play no unimportant part in distributing the air which 

 has entered the leaf through the walls of the epidermal cells. 

 They perform at all events a very obvious and noteworthy function 

 in forming the intercellular spaces beneath the stomata in Pinus, 

 and in producing air channels between the cells forming the 

 several rows of the palisade tissue ; but whatever functions they 

 perform are mainly the result of adaptation on the part of the 

 leaf to derive the greatest possible advantages from their presence 

 when they first occurred, and the leaf having become so adapted 

 in a favourable manner their existence was perpetuated. The 

 results which I have obtained as to the conditions under which 

 the pseudo-ingrowths are developed seem to me to have con- 

 siderable general importance as pointing out the existence of 

 an intimate connection between the nucleus and the cell-wall such 

 as Strasburger and Schmitz have shown to be present between the 

 protoplasm and the latter. 



The cells of the cortical ground tissue contain numerous 

 chlorophyll grains, and after treatment with absolute alcohol to 

 dissolve out the pigment, the protoplasmic basis of these then 

 exhibits the reticulated organized appearance first described and 

 figured by Pringsheim 1 . No spongy tissue is present. 



The resin-ducts — passages — or canals. These run parallel to 

 the longitudinal axis of the leaf and their number is not very 

 constant ; a pair of large ducts are however constantly present 

 just below the angles of the leaf where the upper and lower leaf 

 surfaces join one another. These Kreuz, who has made a careful 

 study of the comparative structure of the resin-ducts in the Conifers 



1 "Ueber Lichtwirkuug und Chloropbyllfuuctiou in tier Pflauze," Pringsheim's 

 Jahrbiicher fUr icissenschaftliche Botmiik, Vol. xn. 1881. 



