INTERCELL ULAR SPACES. 



129 



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



e.g., 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 

 Reservoirs 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 reservoir s. 

 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 Fig. 114.-Part of the transverse section throneh th 

 11 4. internode of the stem of Potamogeton pectinatite. show- 

 Cells S0011 Separate in? the large intercellular spaces between th- central 

 from P'ipli nthpr in fibro- vascular bundle and the circumference of the stem : 

 IlOIIiedCn Otliei in epidermis; a, a small handle. consigns of mirronnd- 

 thp 'ivis nf flip nnl ing fibrous tissue and a vnry s.ma'1 central mas of sieve 

 * tissue: b, b. b. small bundles containing only fibrous do- 

 ll 11111 and fhim sue; ** hmidle sheath of principal hnndli'in the axis of 

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

 form a Small Canal ing the intercelllllar canal, g. X 80. -After DeBary. 



(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 



