lf> ORGANOGRAPHY. 



BOOK I. 



are those of a spiral vessel. That the partitions really exist, 

 as has been correctly stated by Dutrochet, there can be 

 no doubt, notwithstanding the denial of the fact by Link and 

 others. They may be seen with the naked eye in tlie vasiform 

 tissue of the Cane, the Bamboo, and many other plants. 



Vasiform tissue is therefore to be considered composed of 

 cy:indrical cells, the sides of which are covered with oblono- 

 granules, looking like dots, and arranged with their principd 

 axis across the tube, and the united ends of which cause the 

 partitions discoverable upon a longitudinal section. It is these 

 partitions, moreover, that produce the external appearance of 

 transverse transparent lines. 



Slack takes, howevei', a somewhat different view of the 

 nature of the dots. He considers them to be transparent 

 spaces in the sides of the cells, and caused by the separation, 

 at intervals, of a spiral fibre whose convolutions are partially 

 and firmly united in the spaces between the dots ; and he re- 

 presents a case of vasiform tissue from Hippuris in illustration 

 of his position. This is a very ingenious explanation, and 

 perhaps the true one, of what is a most puzzling circumstance, 

 if the dots are really granules, viz. the great regularity with 

 which they are arranged. But it requires further confirm- 

 ation. 



The vasiform is the largest of all kinds of tissue. The holes 

 which are so evident to the naked eye, in a transverse section 

 of the oak or the vine, are its mouths; and the large openings 

 in the ends of the woody bundles of Monocotyledonous stems, 

 as in the Cane, are also almost always caused by the section 

 of vasiform tissue. The stems of Arundo Donax, or of any 

 larger grass, is an excellent subject for seeking it in; it can be 

 readily extracted from them when boiled. 



In the centre of some of the bladders of the cellular tissue of 

 many plants there is a roundish nucleus, apparently consisting 

 of granular matter, the nature of which is unknown. It was 

 originally remarked by Francis Bauer, in tlie bladders of 

 the stigma of Phaius Tankervilliae. A few other vegetable 

 anatomists subsequently noticed its existence ; and Brown, 

 ni his Memoir on the mode of impregnation in Orchidea> and 



