INTERCELLVLAK SPACES. 



139 



cellular ; of this nature are the cavities in many hollow stems 

 — e.g., in many XJmbelliferaB and Gramineae. 



162. — There are in many plants intercellular spaces and 

 canals which are made the receptacles for special secretions, 

 and to which the 

 name of Secretion 

 Eeservoirs niay be 

 applied. They are 

 surrounded ( at 

 first, at least) by 

 secreting cells, 

 which furnish the 

 oil, gum, resin, and 

 other substances 

 (seep. 63) found in 

 the reservoirs. 

 Their structure 

 and mode of de- 

 velopment may be 

 illustrated by the 

 gum-canals of the 

 Ivy {Hedera helix). 

 Each at first con- 

 sists of a long col- 

 umn developed in 

 the phlo6m, and 

 composed of four 

 Or five rows of thin- 

 walled cells arrang- 

 ed radially about a 

 common axis. The 

 cells soon separate 

 from each other in 

 the axis of the col- 

 umn, and thus 

 form a small canal 

 (Fig. 115, A), which is afterward increased in diameter by 

 the formation of radial partitions, and the tangential growth 

 of the surrounding cells (Fig. 115, E). The surrounding 



Pig. 114.— Part of the transverse section thronsh the 

 intemnde of the stem of PotamOQeton pectinatm, show- 

 inff the lars^e intercellnlar spnces between the central 

 fibro-vapcularbnndle and the circumference of the stem ; 

 fi, e. epidermis: a. a small bundle. consisHngrof surronnd- 

 ins fibrons tissue Mnd a very small central mass of sieve 

 tiesne: 6, 6, ft, small bundles containing: only fibrons tis- 

 ene ; w. bundle sheath of principal bundle in the axis of 

 the stem, within which is a mass of sieve tissue surround- 

 ing the intercellular canal, g. x 80.— After De Bary. 



