74- SPIRALS SITUATION. [BOOK i. 



already explained (p. 55) ; in the latter, they are apparently 

 of an intermediate nature between the fibro- cellular and the 

 vascular; agreeing with the former in size, situation, and 

 general appearance, but differing in being capable of un- 

 rolling. Such tissue is, in fact, very common in the skin of 

 seeds, where also true spiral vessels occur when the skin is 

 traversed by veins. Mr. Quekett observed that, if you place 

 almonds in boiling water, and separate the testa, and while 

 thus softened scrape or remove some of the veins which figure 

 its surface, it will be found that the veins are almost wholly 

 spiral vessels, which are of rather minute dimensions. In 

 the stem of Endogens, spiral vessels occur in the bundles of 

 woody tissue that lie among its cellular substance ; in the 

 leaves of some plants of this description they are found in 

 such abundance, that, according to De la Chesnaye, as quoted 

 by De Candolle, they are collected in handfuls in some islands 

 of the West Indies for tinder. The same author informs us 

 that about a drachm and a half is yielded by every Plantain 

 (Musa), and that the fibres may be employed either in the 

 manufacture of a sort of down, or may be spun into thread. 

 In Coniferous plants they are few and very small, and in 

 flowerless plants they are for the most part altogether absent; 

 the only exceptions being in Ferns and Lycopods, orders 

 occupying a sort of middle place between flowering and 

 flowerless plants: in these they no doubt exist. The late 

 Mr. Griffith has succeeded in unrolling them in the young 

 shoots of Lycopodium denticulatum, and Mr. Quekett in 

 Diplazium seramporense. 



Dr. J. W. Griffith has described a peculiar modification of 

 the true spiral vessel in the petioles of some British ferns. 



These tubes are described as being situated in bundles at 

 tolerably regular distances from the axis and from each other, 

 surrounded by the cellular system of the petiole. In the 

 younger petioles they are mixed with spiral vessels, but these 

 are rarely found in the older ones. Their transverse section 

 shows them to be cylindrical or elliptical, not angular nor 

 solid. They are usually of a yellowish brown colour, termi- 

 nating in acute extremities, which become more obtuse as 

 their age advances. In situ their terminations overlap 



