compared with other genera of Cycadeae. 617 
of small, scattered segments, consisting of equal parts of 
xylem and phloem, and either abutting directly on the phloem 
of the first anomalous ring, or separated therefrom by a few 
layers of parenchyma. 
3. The presence of a tertiary cambium which, arising in 
isolated places in the parenchyma either between the normal 
and the first anomalous ring, or between two anomalous rings, 
forms wood and bast with inverted orientation, such that its 
xylem is usually directly opposite that of one of the segments 
of an anomalous ring. This orientation of the bundles, 
especially in those near the normal ring, is, however, subject 
to the variations described in the foregoing pages, as is also 
the amount of tissue formed by this cambium. 
4. The irregularity and displacements of many portions of 
the vascular tissue, owing to the great expansion of the 
parenchyma and the medullary rays between the various 
segments composing the rings. 
The occurrence of the anomalous zones of thickening and 
of a tertiary cambium producing bundles with inverted orienta- 
tion in this stem, can scarcely be passed over with a bare 
statement of the facts. I have been much struck with the 
appearance of these structures, especially after comparing 
them with anomalies in the stem of Cycas, and have therefore 
deemed it worth while to put forward a few considerations with 
regard to them, before drawing this paper to a close. 
It appears to my mind highly probable that these structures 
have a phylogenetic and not a merely physiological significance. 
I would emphasize the great similarity existing between the 
structure, such as that represented in Fig. 12, and that of 
a concentric cauline bundle of Cycas. There are the same 
* transfusion-tracheides 5 between the two oppositely-orien- 
tated strands of vascular tissue, a fact which seems to show 
that the parenchyma separating the two strands in Macrozamia 
is identical with the so-called pith of the cortical bundles in 
Cycas. 
The whole structure, both of the anomalous zones and the 
tertiary cambiums, recalls strongly that of the stem of the 
T t 
