Macrozamia heteromera, Moore. 7 



namely that the phloem conducts food to the cells surrounding 

 the duct, so as to enable them to secrete mucilage. These two 

 explanations are not, however, mutually exclusive, and the phloem 

 of the pith bundles may serve to fetch or to carry according to 

 the needs of the plant. In a paper on the gum of Cycads 

 published in 1839 Morren 1 gives some reasons for supposing that 

 the substance is not stationary, but has an ascending motion in 

 the stem, at least at the time when the young leaves are 

 developing. His curiosity was first aroused by noticing the great 

 length of the gum "boudins" which gradually exuded from cut 

 petioles. He performed a number of experiments, of which the 

 following seems to me the most suggestive. On a Cycas revoluta 

 in full vegetation he made cuts in the rachis, perpendicular to the 

 axis, 2 inches apart. He removed half the thickness of the 

 petiole between these cuts, and thus made a kind of canal in 

 which he might intercept the gum in its passage. He found that 

 the gum always came from the stem side, and never from the leaf 

 side of the cut. His final conclusion is: — "La gomme est, dans 

 les Cycadees, une matiere formee au detriment de la fecule de la 

 tige, et montant par une progression ascendante de la tige dans 

 la feuille." 



(vi) The Roots. 



At the bottom of the stem there were numerous bases of dead 

 adventitious roots, and part of one root in good condition. The 

 latter was diarch, and had a slender plate of primary xylem, 

 consisting, as seen in transverse section, of two protoxylem groups 

 connected by scattered metaxylem tracheids. A large fan of 

 secondary xylem arose on each side of the primary xylem. These 

 fans, at least in part of the root, were unsymmetrically developed, 

 so that a deep bay of parenchymatous tissue was left opposite one 

 protoxylem, and a shallow bay opposite the other. This recalls 

 the want of symmetry mentioned by Brongniart 2 in the lateral 

 roots of Cycas circinalis, and ascribed by him to mutual pressure, 

 A band of secondary phloem occurs on the outer side of each of 

 the two groups of secondary xylem, and a little of what appears 

 to be crushed primary phloem is recognisable. The conjunctive 

 tissue and parenchyma of the stele are extraordinarily rich in 

 calcium oxalate crystals and cells containing tannin and gum. 



Some of the parenchymatous cells shew peculiar brown con- 

 tents. These are generally more or less contracted away from the 

 walls of the cells and appear to contain a number of colourless 

 spheres. These vary from tiny spots which only look like pin 



1 Bull. Acad. Roy. des Sci. Brux. Tom. vi. Part n. p. 135. 



2 Ann. Sci. Nat. Ser. in. Vol. v. 1846, p. 21. 



