532 
Note. 
xylic structure as the bundles in the stem of Lyginodendron , or the 
foliar bundles of Cycadeae. The essential difference from Lyginoden- 
dron consists in the fact that in Heterangium these bundles are 
united by the axial xylem, which extends throughout the whole 
interior of the stele. The primary tracheides, with the exception of 
those adjoining the protoxylem, have numerous bordered pits. 
4. The Secondary Tissues . — The secondary wood, when present, 
has essentially the same structure as in Lyginodendron. Cambium 
and phloem, in the normal position, are fairly preserved in some of 
the specimens. 
5. The Cortex .— The most characteristic feature here consists in 
the horizontal plates of sclerotic cells in the inner cortex. Their 
structure is precisely that of the ‘ stone-cells/ found in the cortical 
tissues of many recent plants. Their presence in the cortex of the 
stem is a point of difference from Lyginodendron , where the sclerotic 
masses are usually limited to the pith and pericycle. 
6. Branching of the Stem . — In one specimen a young stem bears 
a branch much smaller than itself. This is the only distinct case of 
branching observed in either genus. All other supposed branches 
have turned out to be either petioles or adventitious roots. 
B. The Leaf. 
1. Connexion between Leaf and Stem . — The bases of petioles, in 
connexion with the stem, have been observed both in transverse and 
longitudinal section. These specimens show that the cortical tissues 
of the petiole have the same characteristic structure as those of the 
stem ; we are thus enabled to recognize the petioles of Heterangium 
Grievii when detached from the stem. Unlike Lyginodendron , the 
petiole of H. Grievii usually receives from the stem a single bundle 
only. 
2. Form and Structure of the Leaf— Tit find innumerable portions 
of petioles, varying from 4 mm. to 0*4 mm. in diameter, sometimes 
branching, and intermixed with fragments of leaflets. We can only 
infer that the leaf of H. Grievii was a highly compound one, probably 
not very different from that of Lyginodendron. 
The petiole is traversed by a single bundle of concentric structure. 
Thus the bundles underwent the same change on entering the leaf as 
in Lyginodendron. 
