152 



SECRETORY CANALS 



(e.g. by the wind) leads to momentary distortion of the secretory 

 space and consequent emission of part of the secretion. In the 

 Mallows (Malva spp.) many parts of the plant contain irregular 

 lysigenous cavities due to the confluence of cells with muci- 

 laginous walls. 



In many plants, and especially in the stems and roots, the 

 secretions are present in elongated structures, the secretory canals, 

 which are generally schizogenous in origin, the bounding epithe- 

 lium being developed throughout their entire length. In cross- 



~-r ^^^^g^sS-JMS^^^yO* i 



FIG. 76. Secretory organs. A, Lysigenous secretory cavity of the Clove 

 (Eugenia caryophyllatd). B, Schizogenous secretory^canal of the Ivy 

 (Hedera helix) in transverse section. 5., secretory epithelium ; Sc., 

 sclerenchyma sheath. 



sections these canals appear as rounded (Fig. 76, B) or oval 

 cavities, whilst in longitudinal sections they are seen to be 

 extensive sinuous tubes which frequently branch and fuse, thus 

 forming a system often pervading all the parenchymatous tissues 

 of the plant. The secretory canals are commonly (e.g. leaf of 

 the Scotch Fir, Pinus sylvestris ; petiole of the Ivy) enveloped 

 by a sheath of thick-walled cells (Fig. 76 B, Sc.), which prevents 

 compression or collapse through turgor of the surrounding tissue. 

 They often occur in the immediate neighbourhood of the phloem 

 of the vascular bundles, as in the Ivy (Hedera helix) and the 



