1883.] development of the Leaves of Pinus Silvestris L. 353 



species of Adiantum and Aspidium, where they are arranged quite 

 irregularly, occurring on all the walls and having no definite rela- 

 tion to the surface of the leaf: their direction is therefore by no 

 means constant 1 . 



Their presence is by no means uniform even in the same genus, 

 for they are absent from the leaves of Anemone silvestris, though 

 present, as has been mentioned, in other species ; and they are 

 wanting in Alstroemeria bicolor and A. aureum though present in 

 A. psittacina. They are further not absolutely confined to palisade 

 tissue although they are of very characteristic occurrence there, for 

 in Bambusa Simonii, Haberlandt found them prevalent in the cells 

 of the sub-epidermal layer of the under surface of the leaf as well 

 as in the two rows of palisade cells on the upper surface. Very 

 frequently in the same leaf and even in the same section ordinary 

 palisade cells occur at intervals among palisade cells characterized 

 by the presence of these pseudo-ingrowths e.g. in many Ranun- 

 culacese, in Elymus canadensis, and in Todea aspera. I have 

 examined the development of these pseudo-ingrowths in the leaves 

 of several of the species in which they were discovered by 

 Haberlandt and Kareltschikoff, and have in all cases found that 

 they have a mode of origin similar to that which I have already 

 described for those of Pinus. In all cases they bear a definite 

 relation to the nucleus, which is placed in close proximity to their 

 internal ends, and with which they are connected either by proto- 

 plasmic or cellulose strands. The chlorophyll corpuscles are always 

 very numerous in the protoplasm (primordial utricle) lying along 

 both sides of each pseudo-ingrowth just as they are on the lateral 

 walls of the cell. 



Haberlandt in the most recent of his two papers draws some 

 curious, interesting, and somewhat startling conclusions as to the 

 physiological significance of the pseudo-ingrowths, and the probable 

 conditions which determined their origin. He considers that the 

 cells which possess them furnish the clue to the main function of 



1 I have been unable to confirm Haberlandt's observations as to the relative 

 direction of these ingrowths in Pinus silvestris, the species which we both alike have 

 examined. His account is as follows: "In the innermost palisade cells nearest 

 the colourless medullary tissue the folds show no definite arrangement in relation to 

 the surface of the leaf ; but the nearer the cells lie to the periphery of the leaf, the 

 more the folds endeavour to assume a position perpendicular to the surface even 

 when, as often happens, they have thereby to make a sharp angle with the wall of 

 the cell on which they occur. The external cells lying under the sub-epidermal bast 

 layer (hypoderma) show folds perpendicular to the upper surface of the leaf. Two 

 folds are at most present in each cell which project opposite one another into the 

 lumen of the cell, and so produce an H shaped cavity." I have found, on the 

 contrary, as many as five or more pseudo-ingrowths, even in the sub-hypodermal 

 cells, which are very frequently no* H shaped ; some of these folds are parallel to 

 each other while some spring from the lateral walls, but I have never been able to 

 observe any definite relation such as that just described, although I have carefully 

 looked for it. 



