ANATOMY OF CERTAIN SPECIES OE ENCEPHALARTOS. 447 



Throughout the stem and, at least in tlie upper portion, in more than one of the zones, 

 the younger sieve-tubes of the phloem exhibit on their oblique terminal or radial walls, 

 as seen in transverse section, distinct traces of callus on the sieve-plates, stained with 

 a watery solution of aniline blue, although this substance appears to be mucJi less 

 frequently present in the lower and older than in the upper and younger part of th(^ 

 stem. 



Although the character is one found also in Macrozamia, I consider it important to 

 state that the curious, irregularly-shaped tracheides described in that plant and in Ci/cas 

 also occur here, scattered amongst the cells of the ground-tissue and the sclerides, on the 

 inner side of the xylem between two successive vascular rings. These tracheides I regard 

 as homologous with the tracheides occupying the centre of the concentric vascular strands 

 in the cortex of the stem and root of Cycas, and of tliose strands wliich constitute^ the 

 chief vascular structure of the MeduUosea?. 



Owing to the early obliteration of the protoxylem elements as seen in the case of the 

 innermost vascular zone, no criterion must be sought from the (apparent) absence or 

 presence of protoxylem in the outer zones as to the primary or secondary origin of the 

 latter. This important point can only be satisfactorily settled by reference to the upper 

 part of the stem near the apex, where the second vascular zone can clearly be ol)served 

 to originate in cambial divisions arising from the parenchymatous tissue immediately 

 outside the phloem of the primary vascular zone, and which Costantin and Morot 

 determined to be the pericycle *. 



A point which was not observed in Macrozamia is the fact that the cambiums of most 

 of the Tascular zones appear to be all active at the same time, for, in at least three or 

 four out of the five zones, narrow and extremely thin-walled cells, with very conspicuous 

 nuclei, were observed, both cell-walls and nuclei staining deeply with hocmatoxylin. 

 This seems to point to the fact that the cambiums of the older zones, as that of each 

 successive new zone arises, do not cease to be functional (at least in this instance), as has 

 been stated to be the case by various authors for other plants, but rather that new 

 elements are added to all or most of the zones simultaneously for a prolonged period. 



An important and, indeed, the only apparent difference between the structure of the 

 stem of this genus and that of the stem of Macrozamia Fraseri, Miq., is the absence, or 

 apparent absence, in the former of the highly interesting tertiary strands with inverted 

 orientation, whose character and homologies were fully discussed in my former paper. 

 Although careful search was made, I could detect absolutely no trace of any such 

 structure in this stem. This does not, however, preclude the possibility of their being 

 present in some other species ; and it is quite probable that they would not be found in 

 all species of Macrozamia. 



In the larger meshes of the network exhibited by a tangential section of the phloem of 

 any of the vascular zones are seen the leaf-trace bundles accompanied always by a 

 mucilage-canal, the latter passing right through to the pith, for there is a coiitinuons 

 system of these mucilage-canals throughout the entire parenchymatous system of the 



* EuUetin de la Sociote Botanique de France, xxsii. Ib85, pp. 17^i-175. 



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