v 
70 ON THE SEXUAL ORGANS OF THE CYCADACEZ, 
edges. The same structure may be recognized in the biovular carpo- 
phylls of other Cycadacee, and we see that in them the flattened form 
gives rise to tetragonal forms in consequence of the opposing mutual 
pressures. 
6. Anatomically the ovule resembles a thickened leaf-segment, in 
which the tissues are arranged round a centre instead of being drawn 
out ina plane.* I pointed out this homology in 1842 (Monog. p. 12), 
and Heinzel (Diss. de Macrozamia) has taken a similar view. 
The external layers of the carpophyll are composed of parenchyma, 
becoming more merenchymatous in the interior. At the same time 
elongated cells with thickened walls frequently appear in this region.t 
The same arrangement of the tissues occurs in the coat of the ovule in 
every Cycad which I have examined. The two layers, as I have else- 
where shown,} and as is now generally admitted,§ form morphologi- 
cally only a single coat. The external coat, which is filled with juices 
later on, is green when young, but frequently coloured red when ma- 
ture. The internal layer represents the more prosenchymatous part of 
the carpophyll It soon becomes woody, the points where afterwards 
what are called the sutures occur, becoming so last. The two layers 
are reduced to their least thickness in the tubular exostome at the 
summit i both play a more or less important part in the formation of 
* M. Casimir de Candolle in a recent paper on the theory of the leaf 
(Archives des ra: nees, May, 1868, — in ‘Student,’ Aug. 1868), con- 
siders leaves as branches with the side turned towards the axis undeveloped. 
The ovules ies Create may be looked upon as dom o a more complete 
stru € of particular portions of the carpophyll.—W 
other dios it then VM Har pid diverges a 1 little from the leaf (see 
above, me pa s in Pringsheim’s Jahrb. t. iv). 
es "mafia inteqgumenti md et E ab illa pain qualia hucus- 
que Nm aliquo vede, M rsa. Inde ab initio offer! 
“1. Stratum externum carnosum, cellulis parenchymaticis regularibus con- 
rene e epi "Pisis ac carpophyllum vestitum . .. . , apex hujus strati 
tubul 
"n ur atum secundum, ligneum vel osseo-ligneum, cellulis parenchymaticis 
et elongatis compositum, materia deposita inde a prima origine lignescenti- 
bus." 
X 
I quote this Pn: becavse an entirely different opinion has been recently 
Sr oen to me (C. A. J. A. Oudemans in Vers. en Meded. der Koninkl. 
Akad. vol. ii. p. 255, et Arch. Néerl. vol. p. 395). The fact that the two 
layers are entirel blended and are boten simultaneously is sufficient to 
show the absurdity of regarding them as two distinct coats, 
does not form a distinct structure, it seems more fane wa ek of it asa 
tubular exostome. 
