Young Plant of Macrozamia Fraseri . 581 
during further growth, gradually assume an almost horizontal position’ 
(Mettenius ] ). 
We have here the normal leaf-supply characteristic of a large leaf with 
broad base. The nearly horizontal course of all the strands of the trace is 
due to the telescoping of the axis ; in the case of the marginal traces, this 
course is necessarily tangential also, on account of the origin of these 
strands from the distal half of the axis, associated with the broad leaf 
insertion. The removal of these ‘ girdles ’ to the periphery of the stem is 
due to the subsequent increase in parenchymatous tissue of pith and 
cortex, as also is the virtual intercalation of radial portions near their 
insertion on the axis. 
(ii) The Anomalies of the Vascular System, 
The anomalous rings. The result of this investigation harmonizes 
two divergent views. Some workers have derived the anomalous rings 
from a pericyclic cambium. 2 others from branches given off from the 
normal ring. 3 It is seen that, in Macrozamia Fraseri , both factors play a 
part in their development. 
It is established that, in the plants under examination, the appearance 
of the anomalous ring, at any point in the stem, is preceded by two 
occurrences which have possibly a physiological significance. 
(1) Starch depletion of the inner cortical tissues. 
(2) Tangential extension of the tracheides and phloem elements being 
formed by the cambium of the normal cylinder. This tangential elongation 
is probably the result of that definite horizontal growth established near 
the stem apex, 3 while the horizontal growth is itself the result of those 
environmental conditions which have imposed slow growth and the tuberous 
geophilous habit on these plants. The task of supporting large leaves on 
a very shortened axis would seem to make a broadening of this axis 
intelligible. This adaptation would bring other difficulties in its train ; one 
result already attributed to it is the complication in the course of the strands 
entering the mature leaf. Another result would probably be strain on the 
established tissue beneath the apical zone, and a consequent stretching of 
the non-lignified elements along the line of least resistance. To some such 
sequence of events the gradual extension of the cambial elements and the 
tissues derived from them is probably due. That this would not react 
favourably on conduction seems evident, and the starch-depleted layer 
developed at this point in the cortex possibly reflects a functional starvation 
of that tissue, whether due to this distortion or to the general inadequacy 
1 Mettenius : loc. cit. 
2 Constantin and Morot : Sur l’origine des faisceaux liberoligneux surnumeraires dans la 
tige des Cycadees. Bull. Soc. Bot. France, xxxii. 173, 1885. 
3 Matte : loc. cit. 
