INTERCELLULAR SPACES. 



129 



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



e .g m} in many Umbelliferse 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 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 cella arrang- 

 ed radially about a 



Common axis. The Fig. 114. Part of the transverse section through the 



11 ca-nnvata Internode of the stem of Potamoaeton peotinatus, show- 



CC11S SOOn Separate \ n s the large intercellular spnces between the central 



fiT>m oar>V> /-kfhov in fibro- va scular bundle and the circumference of the stem/ : 



1 e, e, epidermis; , a small bundle, consisting of enrronnd- 



+Vio Qvia rtf fno nnl ing fibrous tissue and a very small central mass of sieve 



tissue ; b, b, b. small bundles containing only fibrous ti- 



UTTin and fVm me '< u < bundle sheath of principnl bundle in the axis of 



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



form a small Canal ing the intercell " Iar canal, g. x SO. 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, E}. The surrounding 



