212 M. B. WELCH. 



enlarged cavity encroaching on the surrounding paren- 

 chyma. It would thus appear that the oil in this case is 

 the outcome of the alteration of the already present cell 

 contents. 



There are three methods by which secretory cavities 

 can be formed, namely: — 



(1) lysigenous i.e., breaking down of the secretory cells* 



(2) schizogenous i.e., separating apart of the secretory 



cells. 



(3) schizolysigenous i.e., a combination of the first two. 



Although Haberlandt, (Plant Anatomy, p. 516), and others 

 state that the secretory cavities in the Myrtacese are 

 characterised by the schizogenous mode of formation, the 

 evidence of the Eucalypts seems rather to indicate the 

 third method, i.e., schizolysigenous, as far as this genus is 

 concerned. It might be mentioned in passing, that the 

 early gland development in some of the Rutacese (which 

 Order Haberlandt (7.c, 516), places in the lysigenous group) 

 shows an apparently identical structure to that found in the 

 early stages of E. Smithii. De Bary regarded the Myrtace- 

 ous gland as being lysigenous in origin. 



Again, according to Haberlandt (I.e., 517), the secretory 

 tissues of a schizogenous gland generally consist of a single 

 layer of glandular cells, which are almost always readily 

 distinguishable from the cells of the adjoining tissues in 

 their form and contents. 



Solereder, (Syst. Anat.) does not regard the presence of 

 an epithelium lining the fully developed cavity as being 

 conclusive proof of a schizogenous origin. In the Eucalypts 

 so far examined, -(over fifty species) an epithelial layer is 

 not a conspicuous feature. 



The discharging mechanism of the gland is also important. 

 Porsch, working on E. globulus and E. pulverulenta found 



