34 ELEMENTARY ORGANS OF PLANTS. 



34. Spiral fibre usually consists of a single filament, but 

 sometimes numerous fibres are united together, assuming the 

 aspect of a broad ribbon or band, as may be seen in the stems 

 of the banana or the asparagus. When the spiral coil re- 

 mains unbroken, it is so strong and tough, in comparison with 

 the delicate cell-wall on which it is deposited, that it may be 

 torn out and uncoiled when the vessel is pulled asunder, the 

 membrane being destroyed in the operation. This capability 

 of being unrolled characterizes the true spiral fibre. 



35. Spiral fibre is soon known, and familiarized to the 

 mind, by breaking asunder almost any young shoot or leaf- 

 stalk (as for instance that of the geranium or strawberry), 

 and gently separating the broken ends, when a number of 

 white glistening fibres of extreme delicacy, and not unlike 

 the threads of the spider's web, will be seen running from 

 one portion to the other. If these threads be placed under 

 the microscope, it will be evident that they had lain in spiral 

 coils, which are partially straightened through being drawn 

 out, just as when a spiral spring is strained. These vessels 

 were first discovered by Henshaw, in the year 1661. 



36. Vascular tissue is never wholly filled up by deposits 

 of sclerogen, the spiral fibre within it keeping the canal of 

 the tubes constantly open. The accurate experiments of 

 Bischoff have led to the conclusion that the perfect spiral 

 duet or spiral vessels are filled with air which contains a large 

 amount of oxygen in its composition. This oxygen, the 

 result of the chemical compositions and decompositions going 

 on in the interior of the plant, spiral vessels convey from the 

 central part of the plant to its young shoots and leaves, the 



