26 



THE \ASCULAR TISSUE. 



all flowering plants, but more so in certain bulbous plants, as that of a squill growing in 

 the neighbourhood of the Mediterranean. The inhabitants collect them, and tie them in 

 bundles to be used in the lighting of cigars an office for which their smouldering flame 

 renders them well adapted. They are met with in all parts of plants except the roots, 

 but more particularly immediately surrounding the pith, and in all parts emanating 

 from it viz., branches, leaves, flowers, and fruit. They may be readily obtained 

 by cautiously cutting through the cuticle of the footstalk of the strawberry -leaf (Fra- 

 ffctria'), and then gently separating the divided^ portions, when they appear as very 

 fine threads arrange:! in loose spires. 

 They abound in the veins of leaves, 

 and even in the minutest parts of the 

 most delicate flowers. They are also 

 found in the foot-stalks of all fruits, 

 and in the vascular bundles which 

 enter the minutest seeds. This may 

 readily be seen by tearing the seed 

 of the strawberry from the fruit, 

 and placing it in water under the 

 microscope. The spiral vessel is 

 there exceedingly minute and beau- 

 tiful. 



Perhaps, of all positions in which it Fig- 66> _ A por t ion of a bund i e O f spiral vessels from 



may be the best inspected, that of the the stem of the potato plant (Solatium tuberosum), 



., , embedded in loose cellular tissue, as represented at a. 



veins running over the brown coat- The tubular character of the tissue is well seen at 6, 



ing of the common hazel nut ( Corvlus where the separation of the fibres permits the observer 



77 I?- ^K\ L J.T- i MI to look within the tube. At that point also the in- 



MMUfHUjJtlg. bo), alter the shell has closing membrane is well delineated. These are 



been removed, is the most accessible of lar ^ e size > and > with tQOSe of Fi - 65 ma l wel1 re - 

 mi -, , present the two extremes of development. Magnified 



Ihe brown membrane should be 200 diameters. 



soaked in water for a short time, 



and then the veins carefully torn open with needles, and placed under the microscope. 

 If the light be not passed through them, but be allowed to fall upon them, they 

 appear as bundles of beautifully- white glistening lines, consisting of scores of very 

 minute spires. 



Such is also the case with other similar fruits, as those of the walnut (Juglans 

 regia] and chestnut (Fagus castanea). They are seen to great advantage also in cer- 

 tain succulent stems, as those of the potato, by cutting the stem across obliquely 

 with a knife in bad condition, and the section placed under the microscope (Fig. 66). 



They are of very delicate structure, and require other tissues to inclose and protect 

 them. This is chiefly performed by the woody fibre, and thus each vein of a leaf or 

 herbaceous stem has its central bundle of spiral vessels inclosed in a covering of 

 woody fibre. 



The use of the spiral vessel has been the subject of much investigation, and it 

 appears probable that at some period it conveys air charged with an increased per 

 centage of oxygen, and thus becomes a system of internal respiration, much after the 

 manner of the distribution of the trachea? in insects. At a later period of its existence 

 it is probable that it contains fluid. The spiral fibre is valuable at either of these 

 periods as keeping the tube open, but more particularly when the cavity is filled by 

 air only. 



