LinruBan Society. 49 



the appearance of being marked with transverse stripes. The 

 vessels in all present so much similarity, that no generic distinction 

 can be drawn from them. The dots are always arranged dia- 

 gonally. The dotted vessels of Zamia furfuracea and pumila 

 were observed to unroll spirally in the form of a band, pre- 

 senting a striking resemblance to those of Ferns. The band was 

 found to vary in breadth in different vessels, and was furnished 

 with transverse rows, composed of two, three, or more dots. The 

 coils followed the direction of the dots, and the unrolling was from 

 right to left. In Cycas revoluta dotted vessels frequently occur with 

 a single row of dots; but, from the circumstance of the dots on botli 

 sides being in view at the same time, they are liable to be mistaken 

 as having a double row on each side. Besides the dotted vessels, 

 there occurs throughout Cycadece another variety, differing but 

 little from the ordinary spiral vessel, except in the tendency of the 

 coils to unite. In some vessels the coils are free, and the fibre ex- 

 hibits frequently, at intervals, bifurcations or narrow loops ; in others 

 the coils unite at one or both sides, in which case the vessel presents 

 a series either of rings or bars ; the fibre then is with difficulty un- 

 rolled, and it often breaks off into rings, or the bars separate at the 

 point where the coils unite, which is generally on the perpendicular 

 sides of the vessel. In other cases the vessels are distinctly reticulated, 

 and they then exhibit a striking analogy to the dotted cellules mCycas 

 revoluta. All these modifications are frequently to be observed in 

 the same vessel in Zamia furfuracea tini^ pumila, a fact which affords 

 conclusive evidence of the accuracy of the theory advanced by Meyen, 

 which refers the spiral, annular, reticulated, and dotted vessels to a 

 common type. The dots and stripes are evidently the thinnest portions 

 of the tube, being most probably parts of the primitive membrane re- 

 maining uncovered by the matter subsequently deposited on the walls. 



The cellular tissue of Cycadece consists of tolerably regular paren- 

 chyma, composed of prismatic, six-sided cellules. In the species of 

 Zamia and Encephalartos, so often referred to, the walls of the cellules 

 appear to be of a uniform thickness and transparency, and destitute 

 both of dots or markings ; but in the adult fronds of Cycas revoluta 

 a diflferent structure presents itself, for the walls of the cellules are 

 furnished with numerous elliptical, obliquely transverse dots or 

 spaces, where the membrane is so exceedingly delicate and trans- 

 parent as to give to the cellules the appearance of being perforated 

 by holes, the intervening spaces being covered by incrustating 

 matter, disposed in the form of confluent bands, which, when 

 viewed under the microscope, resemble a kind of network. The 



Ann. Nat. Hist. Vol. 5. No. 28. March 1 S40. e 



