1840.] Linnean Society. 55 



rolled, and it often breaks oflF 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 in Cycas 

 revoluta. All these modifications are frequently to be observed in 

 the same vessel 'm. Zamia furfur acea and 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 por- 

 tions of the tube, being most probably parts of the primitive mem- 

 brane remaining 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 different 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 

 dots or spaces uncovered by incrustating matter, are generally of 

 a large size, and occur more particularly on the vertical sides 

 of the cellules, a band usually running along the middle of the 

 two opposite sides. The bands vary in breadth, as do the dots, 

 and they not unfrequently exhibit minute transparent points or 

 spaces where the solid matter forming the band shows a tend- 

 ency to separate. The extreme delicacy and transparency of the 

 dots or spaces of whatever size, appear fully to prove that they 

 are parts of the primitive membrane of the cellule, which are un- 

 covered by the incrustating matter. A solution of iodine will be 

 found of great service in determining the actual existence of the 

 membrane at those parts ; for although it does not materially alter 

 its colour, it tends very much to diminish its transparency and ren- 

 ders it distinctly visible, so as to leave no doubt that the spaces eire 

 not openings. The bands are evidently the result of a partial hgni- 

 fecation ; and indeed no better example can be offered than Cycas 

 revoluta to illustrate and confinn the correctness of the views ad- 



