244 LECTURE XII. 



The waxes are not, like the fats, compound ethers of glycerin, but 

 they are compound ethers of monohydric alcohols with the higher 

 members of the fatty acid series : with these, free acids, alcohols and 

 fats are mixed. Thus the Carnauba wax has been found by Maskelyne 

 and by Berard to consist of 



Melissin or Melissyl alcohol C^H^O 



Cerotic acid or Cerin C^H^O* 



Cerotin or Ceryl alcohol C^H^O. 



Palmitin, Stearin, Laurostearin etc. (fats). 



We will enquire, in conclusion, into the fate of the waste- 

 products. Some of these, such as oxygen, water, and methy- 

 lamin, are excreted in the gaseous form ; the greater part 

 of the carbon dioxide is also excreted as a gas, but some 

 of it combines with earthy bases to form carbonates, which 

 are either retained in the plant, or are excreted in solution : 

 the resins and ethereal oils, as well as wax, are frequently 

 excreted. 



The mechanism of excretion is widely different in dif- 

 ferent cases. The resins and ethereal oils are excreted 

 usually by means of special glandular organs. The gland 

 may be a hair on the surface, and it is then commonly the 

 terminal cell at the free end which is secretory (Fig. 32); 

 or it may be a group of epidermal cells between which large 

 intercellular spaces are formed which serve as receptacles 

 for the excreted substance ; or the gland is formed by the 

 absorption of the adjoining walls of a group of cells belong- 

 ing partly to the epidermis and partly to the underlying 

 ground tissue, a cavity being thus formed which contains 

 the excreted substance: or again, strands of cells may be- 

 come separated so as to enclose an elongated intercellular 

 space into which they excrete ; it is in this way that resin- 

 ducts are formed. In many cases the substance to be 

 excreted may be detected in the glandular cells ; not unfre- 

 quently, however (always in the case of wax), no trace of it 

 can be observed in the cells themselves ; it is first to be found 

 in the cell-walls between the cuticular and the deeper layers. 

 We must not conclude from this, as de Bary points out, 

 that the excretion is actually formed at the expense of the 



