INTERCELLULAR SPACES. 



129 



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

 — e.g., in many Umbelliferse and Graminese. 



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 may be 

 applied. They are 

 surrounded ( at 

 first, at least) by 

 secreting cells, 

 which furnish the 

 oil, gum, resin, and 

 other substances 

 (seep. 62) 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 phloem, 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 



Fig. 114.— Part of the transverse section through the 

 intemode of the stem of Potamoaeton peciinatus. ehow- 

 insr the lare;e intercellular spices hftwpen th** ren^ral 

 fibro-vflscular bundle and the rircumferenre of the stem ; 

 c, e. epidermis; a. a small bundle, consisting: of snrronnd- 

 infr fibrons tissne «nd a vnry small central muss of sieve 

 tissne; 6, b. h, small bundles containing only fibrous tis. 

 sue; w, bundle sheath of principal bundle in the axis of 

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

 form a small canal i"g the intercellular canal, c. x 80.— After De Bary. 



(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, U). The surrounding 



