XO DR. J. D. HOOKER ON THE STRUCTURE AND 



posed of elongated cells whicli are more opaque towards tlie centre of the bundle ; lower 

 dowTi in the peduncle they present the same appearance as is represented in figs. 2G and 27, 

 which shoAV vessels fi-om the apices of the bundles in the rhizome. In fig. 22 some vessels 

 of the rliizome, and on the left the base of one of those of the peduncle, are seen : at this 

 part of their com-se both are regularly banded ; which is better seen in figs. 23 and 24, 

 where they are more highly magnified. Every intermediate form of vessel may be found 

 between those represented at figs. 15 and 27 ; and occasionally in both organs the form 

 of cellular tissue, seen at fig. 25, is found; which appears to be another modification, 

 intermediate between the vascular and cellular, and which, in fig. 23, is placed outside 

 the barred vessels. 



In older specimens of B. involucrata much larger cylindi-ical vessels are found in the 

 rhizome, mixed with hexagonal tubes with barred or otherwise marked sides, and bundles 

 of pleurenchyma, which also occur in the peduncle, but ia a much less perfectly deve- 

 loped state. 



I find considerable uniformity in the microscopical character of the vessels amongst 

 different specimens of B. dioica, although these have grown on widely difi'erent genera of 

 plants (and the same remark applies to Rhopalocnemis) ; and I do not in any case find a 

 more highly developed tissue in the peduncle than in the rhizome. On a comparison of 

 my dissections of young specimens of B. involucrata with Goeppert's of old ones of 

 B. elongata, the differences between them are perfectly reconcilable. Gceppert figures 

 barred cylindrical vessels of cellular tissue as occurring only in the peduncle, and larger 

 vessels with short transverse bars as occurring only in the rhizome ; this I also find to be 

 the case in old specimens ; but in younger ones the barred cylindi'ical vessels are abundant 

 in the rhizome, and comparatively rare in the peduncle ; from which it may be inferred, 

 that the said vessels are an imperfectly developed tissue. 



In full-grown specimens of B.fungom (Plate VIII. fig. 12), the same forms, relations, 

 and modifications of vascular tissue prevail to a considerable extent ; and the same may 

 be said of other species which I have examuied, though less in detail ; whence I conclude 

 that the anatomical differences between the vessels of the rhizome and those of the peduncle 

 are dependent on position and degree of development. 



The rhizome of the most perfect species of BalanophorecR is decidedly exogenous. If a 

 transverse section of the elongated one of Helosis mexicana be taken, the mass will be 

 found to be composed of cellular tissue, enclosing (in the specimen given at Plate XV. 

 fig. 14) a vascular system consisting of seven wedges, Avhich surround a narrow cylindrical 

 axis. Each of these wedges is (on a transverse section) narrow and oblong, and consists 

 of many rows of annulate or transversely barred cylindrical or angular ducts, which 

 occupy the position of the pleurcnchynaa of ordinary exogenous plants ; outside of these is 

 a reniform mass of stout, elongated hber-cells, into whose concave faces the outer ends of 

 the wedges are thrust. Beyond the vascular system is a very thick spongy cellular mass 

 continued to the circumference, where the cells are smaller and denser : this cellular 

 tissue is everywhere interrupted by small masses of thick-waUed sclcrogen-cells, round 

 which the cells of parenchyma radiate, and wluch, in a transverse section, resemble scat- 

 tered liber-bundles. Sui-rounding the axis is a seven-lobed zone of stout sclerogen-tubes, 



