300 



PHILOSOPHICAL ><JTES OK 



Fig. 128. Oil cavities of Dictamuns Frcuinella (Sachs' " Physiology of 

 Plants : (a) early stage, showing breaking down of central cells only, 

 (6) cavity with a drop of oil. 



Sacks says, at p. 183,* *'The oil glands of the Orange and 

 others originate, so far as investigation extends, from a single 

 mother cell, which, as it slowly develops, undergoes many di^-isions 

 in all directions, so that a multicellular mass of tissue of roundish 

 form arises,! the cells of which subsequently become remarkable 

 as containing very granular, apparently dead, protoplasm. Later 

 on, the thin cell walls dissolve, the process commencing in the 

 middle of the spheroidal group, and jDroceeding outwards. There 

 arises a roundish cavity, filled partly with watery sap, partly 

 with drops of ethereal oil or balsam J the products of solution of 

 the mass of cells. The layers of tissue surrounding this cavity fit 

 closely on all sides, without intercellular spaces, and thus form a 

 kind of wall to the receptacle for the secretion." This is well seen 

 in the leaves of Citrus. 



Why Sachs calls it a secretion is not very clear. If the oil 

 comes by a breaking cloivn of cells, it is more likely to be a 

 degeneration. 



O. Penzig, in his '* Studj sugH Agrumi" (1887), p. 53, say.s, 

 " The contents of the single cells which form the oil gland are at* 

 first protoplasm with a high i-efraction, afterwards they are of 

 essential oil, which fills the whole of the cell. By degrees the 

 walls of the central cells are ruptured, and the essential oil fills 

 the centre of the gland. Then the remains of the destroyed cells 

 line the walls of the cavity thus formed, so that in the adult gland 



* " Text Book of Botany." 



f Such as is seen in the development of the anther, for instance. 



J Such as shown in Figs. 127 and 128. 



