170 ON THE STRUCTURE OF THE TISSUES OF CYCADE.E. 



much gratified by finding his previous suspicions fully confirmed : the 

 cellules then being of a uniform transparency, presenting neither bands 

 nor dots, but furnished with a distinct cytoblast or nucleus, which was 

 found to have entirely disappeared from those cellules in which the in- 

 crusting matter was visible, proving that the incrusting matter is formed 

 at the expense of the nucleus. The matter forming the bands is continu- 

 ous, and is evidently not formed by a coalescing of spiral fibres, as some 

 might suppose ; for it is perfectly solid, and shows no disposition to 

 unroll or to break up into fibres. The bands most probably originated 

 form the shrinking up of the incrustating substance, which at first was 

 equally diffused in a fluid state over the walls, and which, from the 

 mere effects of consolidation, aided by the distension, and perhaps en- 

 largement of the cellule, would naturally leave portions of the primitive 

 membrane uncovered. That the dotted and reticulated vessels in Cyca- 

 decs are of the same nature, and originate in a similar way as the 

 cellules just described, there seems no reasonable ground to doubt. 

 The parenchymatous cellules in Cycas circinalis, glauca, and speciosa 

 resemble those of Zamia and Encephalartos , in having their walls of a 

 nearly uniform thickness and transparency, being but rarely furnished 

 with a few eliptical obliquely transverse spaces or dots. The cellules 

 in Cycas revoluta vary both in size and structure, some being three or 

 four times longer, whilst others are still longer and narrower, and fur- 

 nished with more numerous and much smaller dots, which are not con- 

 fined to the sides, but are disposed around the tube. These last, which 

 have been observed also in Cycas glauca and circinalis, present an evi- 

 dent transition to the dotted vessels. 



The whole of the Cycadete are supplied with numerous gummife- 

 rous canals, often of great length, and uniformly furnished with dis- 

 tinct cellular walls of considerable thickness, and which have been 

 accurately described and figured by Professor Morren in a recent me- 

 moir. 



Notwithstanding the analogies presented by their reproductive organs, 

 the author considers the Cycadeee as related to Coniferce only in a re- 

 mote degree, and that they constitute the remains of a class of plants 

 which belonged to a former vegetation. 



