1 7 6 



SPIRAL VESSELS, 



PART II. 



interior walls of the vascular ducts, there are groups 

 of independent spiral vessels of great beauty and 

 elasticity, of which the seeds of the wild clary afford a 

 remarkable instance. They consist of cylindrical tubes 

 with conical extremities twisted into a right or left- 

 handed screw, which can be unrolled without breaking. 

 They are found in the leaves of almost all plants, in the 

 petals and stamens of flowers, in the stalks of all fruits, 



, even in the minu- 



test seeds ; large 

 parallel bundles of 

 them imbedded in 

 hexagonal cellular 

 tissue may be seen 

 in the veins of the 

 kernel of the hazel 

 nut, and they con- 

 stitute the medul- 

 lary sheath which 

 surrounds the pith 

 in trees. They are 

 all hollow, and ca- 

 pable of conduct- 

 ing liquids. 



The laticiferous 

 vessels orvasapro- 

 pria, those which 

 contain the proper 

 juices of plants whether milky or coloured, are ex- 

 ceedingly varied in their forms and arrangement in 

 different plants, and in different parts of the same plant. 

 In the leaves they generally form a delicate capillary 

 network, in the bark they constitute a system of long 

 vascular ducts forming an elongated irregular network 

 pervious to the proper juices throughout; sometimes 

 they are formed of cells joined end to end, and frequently 



Pig. 5. Longitudinal section of stem of Italian reed: 

 a, pith ; b, fibro-vascular bundles ; c, cuticle. 



