FORMATION OF CELLS— TISSUES 325 



taming secretions, though the cells which formed them may have 

 disappeared. 



The glandular tissue may be a solid mass of cells, as in 

 the nectaries of such flowers as FritiUaria ; it may form a 

 passage or cavity, lined with cells and containing the secretion, 

 as m the resin canals of Pinus and other Coniferce, or in the 

 globular receptacles for essential oil in the leaves of the Kue, the 

 rind of the Orange, &c. 



These passages may originate in two ways. In a transverse 

 section of a very young stem or leaf of Pinus, or a stem of 

 Hedera [fig. 700, a), there may be noticed here and there a 

 somewhat conspicuous cell, which divides by longitudinal walls 

 usually into four. These cells are found in longitudinal sec- 

 tions to form columns which are frequently of some length. A 

 transverse section of a little older stem shows in each position 

 a small group of cells which separate from each other, so as 

 to leave a passage in the centre. Longitudinal sections at this 

 stage show that this passage or channel extends the whole 

 length of the column ; by continued separation and multiplica- 

 tion of the number of the cells surrounding the channel, a 

 duct is formed which is hned by a delicate layer that secretes the 

 resinous matter, and pours it out into the passage. This mode 

 of origin is called schizogeiwus. 



In the case of the oil-glands of the Eue, Orange, &c., a small 

 solid group or column of cells is formed from a single cell or a 

 vertical row of cells, by repeated division. The protoplasm of 

 these becomes charged with drops of the secretion, and the cell- 

 walls in the centre of the mass degenerate and break down, leav- 

 ing a cavity filled with the secretion and with the remains of the 

 cytoplasm of the disintegrated cells. Sometimes a peripheral 

 layer does not disappear, so that the cavity remains lined with 

 secreting cells. This mode of origin is termed hjsigenouis 

 (fig. 699). 



Occasionally both these methods may be met with in the 

 formation of a gland. 



Besides these forms of glandular tissue isolated cells or single 

 rows of cells containing secretions are not uncommon. They 

 may contain tannin, mucilage, or other products. They are 

 generally parenchymatous and thin-walled. 



