170 Dr. Griffith on the Dotted Vessels of Ferns. 



appears a black line extending along their surface and sepa- 

 rating the rows of dots (fig. 4. b.). These tubes always con- 

 tain air, except during their earliest periods. Tubes some- 

 what similar to these have been figured by Link* from ferns 

 {Aspidium, Polypodium, &c.f), but they differ from those I 

 have described in having a beaded margin and the dots being 

 opposite each other. 



These tubes are not true ducts, inasmuch as they uncoil 

 without breaking, and contain air ; they cannot be considered 

 as any form of woody tissue for the last-mentioned reason, 

 as well as because the dots have a spiral arrangement. They 

 are not scalariform vessels, as their markings do not extend 

 across the tube, nor are they angular. They agree with spiral 

 vessels in, 1. terminating in pointed extremities ; 2. containing 

 air ; 3. being composed of a fibre or fibres and a membrane ; 

 4. uncoiling elastically. So that although not actually spiral 

 vessels, in consequence of the edges of the fibres not being 

 free but adherent, they are, I think, undoubtedly formed from 

 them, and perform precisely the same physiological functions. 

 This brings us to the question of the transformation of spiral 

 into dotted vessels, which has been so often and so unprofit- 

 ably discussed, inasmuch as even at the present time the 

 highest authorities differ. I believe that all dotted tubes are 

 not formed in the same way ; thus, the reticulated tubes of 

 flowering plants are formed on totally different principles from 

 those of these ferns. I will not tire my readers by discussing 

 this question, as it has been so often done by the best anato- 

 mists and physiologists. I will merely direct attention to the 

 fact of the spiral vessels being found numerous in young pe- 

 tioles or stems, and being more rarely found, at least not in 

 the same abundance, in the older ones ; also to a beautiful mi- 

 croscopic object lately laid before the public by Mr. Kippistf, 

 I allude to the spiral cells (sp. vessels) found upon the testa 

 of the seeds of Acanthodium, Ruellia, &c. When the surface 

 of these seeds is examined by a lens of low power, it appears 

 covered with whitish appressed hairs. These when moistened 

 separate from each other and resolve themselves into spiral 

 vessels which shoot out in the most beautiful manner from the 

 surface. When they are minutely examined by a high power 

 the spiral fibre is distinctly seen : at that extremity farthest 

 from the testa the fibre remains simple (fig. 3. §) ; where (as in 



* Ausgewahlte anatomisch-botanische Abbildungen: Berlin, 1841. 

 •f* Not British species. 



X Transactions of the Linnaean Society, vol. xix. p. 76. 

 § The figures here alluded to are those accompanying Mr. Kippist's paper 

 in the Linnaean Transactions. 



