2 44 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 



