33:2 



RKSIX-SKCRETlXCi III.AXIIS IN SOJIK AUSTRALIAX PLANTS, 



appear bisecting tlie uppermost stalk cell in planes at right angles (Text-%. 5^;). 

 Similar tlivisions are then tVirniecl in the second stalk cell anil ultimately in the 

 basal epidermal cell (Text-tig. 5//). Owing tn the position of the original hori- 



l^^lfl 



Text-fig. 5. — («-/') • Stages in the development of the normal gland of Acacia verniciflua ; 



i, shows commencement of irregular divisions iu the upper tier of the stalk; y, and^, 



types of gland formed by the omission of the second stalk cell, (x t'M). 



Text-fig. 6 — Mature gland of cicada I'crnicijina in which tlie two-tiered nature of tlie 



stalk has been ol)literated by irregular lUvisions during the later stages of 



development, (x 230). 



zontal division, at a level sometimes above that oi' the neighbouring epidermal 

 cells, these basal cells often project for some distance, and appear to form part 

 of the gland (Text-tig. 5ft, i, j). 



In Text-fig. 5ft we have what is |irob:il]ly the normal type of gland, in which 

 each tier of the stalk is made up of four cells. Text-fig. 5 j and A- represent a 

 ty])e of gland often met where the second stalk cell has been omitted. 



With gi'owth of the gland cells, however, an irregular division often takes 

 place in the upper tier of the stalk wliicli is then made up of five or six poly- 

 gonal cells, irregidarly arranged (Text-fig. 5/). When this irregular division 

 proceeds to the second tier of the stalk, the resulting gland liecomes more com- 

 plex, the sliield-like head being supported by an irregular mass of cells in whicii 

 all trace of the two-tiered stalk is obliterated (Text-tig. (i). 



Acacia armata. — During the development of the glandular hairs in ,1. urmata 

 there is marked variation in the sequence and number of cell divisions. This 

 variation is accountable for the number of gland forms which are mingled freely 

 on the surface of the young phyllode. These gland forms resemble one anothei-, 



