Macrozamia heteromera, Moore. 3 



Anatomy of M. heteromera. 



(i) The Apical Region. 



The apex is sunk in a small pit. Transverse sections taken 

 just below the apex shew a structure to which Mettenius's 1 descrip- 

 tion of the apical region of Cycas revoluta applies almost word for 

 word. " The transverse section of a young stem of Cycas revoluta 

 shews at a small distance from the growing point which is sunk in 

 the stem apex, on the boundary between the pith and the cortex, 

 whose cells are filled with starch grains, a ring-shaped stripe of 

 delicate, radially arranged, meristematic cells, the cambial layer." 



(ii) The Pith. 



Near the apex the pith contains mucilage canals, running in 

 every direction (especially radially) and not accompanied by any 

 vascular tissue. Between the levels where the vascular cylinder 

 is respectively 2 - 5 and 2 - 7 cms. in diameter the first traces of 

 vascular bundles make their appearance in the pith. At the lower 

 of these two levels, i.e. where the stem diameter excluding the 

 leaf bases is 6'5 cms., some of the canals have strands containing 

 lignified xylem beside them, whilst others are merely accompanied 

 by a little meristematic tissue, representing the future bundles. 

 The phloem seems always to be turned towards the canal and the 

 xylem in the other direction. The medullary system of canals 

 and vascular tissue thus agrees in origin and arrangement with 

 that described by Worsdell (I. c.) in the case of Macrozamia 

 Fraseri. Close to the base of the stem the medullary bundles 

 become more strongly developed and more complicated in their 

 arrangement. 



(iii) The Vascular Tissue. 



Sections taken near the top of the stem shew a single ring of 

 vascular bundles of the normal Cycadean type. The tracheids are 

 pitted, and I have been unable to detect any with spiral thicken- 

 ings, except occasionally in the very youngest part of the cylinder. 

 At the level at which the normal vascular ring is rather less than 

 5 "8 cms. in diameter, a second ring is seen arising outside it in the 

 form of small separate bundles. There is no clearly differentiated 

 pericycle in the stem, but as these extra bundles arise immediately 

 outside the phloem of the normal ring, their origin is probably 

 the same as that of the supernumerary bundles of Cycas, which 

 Constantin and Morot 2 describe as " pericyclic." Lower down in 



1 "Beitrage zur Anatomie der Cycadeen," Abhandl. Konigl. Sachs. Gesellsch. der 

 Wiss. v. 1861, p. 573. 



2 Bull, de la Soc. Bot. de France, xxxn. 1885, p. 173. 



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