50 Linneean Society. 



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 are 

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

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

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

 vanced by Schleiden as to the origin of the bands and fibres 

 in the cellules and vessels of plants. Being anxious to ascer- 

 tain whether the bands exist at an early period, the author had 

 recourse to the examination of a young undeveloped frond, about 

 two weeks old, and he was 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 dis- 

 appeared from those cellules in which the incrustating matter was 

 visible, proving that the incrustating matter is formed at the expense 

 of the nucleus. The matter forming the bands is continuous, 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 un- 

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

 from 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 distention, and per- 

 haps enlargement of the cellule, would naturally leave portions of 

 the primitive membrane uncovered. That the dotted and reticulated 

 vessels in Cycadeee 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 spcciosa resemble those of Zamia and Encephalartos in having 

 their walls of a nearly uniform thickness and transparency, being 

 but rarely furnished with a few elliptical obliquely transverse spaces 



