704 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
Page. 
2. Course of the Vascular Bundles. . . . we cee da tet a OTE 
3. Primary Structure of the Stele and Leaf- _— Bundles 2 ew ee 748 
4, The Secondary Tissues. « 2 6 a « a y 2 « @ & ¥ ww w = Pol 
5. The Cortex. . . eUGR By SLE es MBL. Sok ot ele (08 
6. Branching of the Siete, a est OR Wu teee Boe oy 4. Ce a oe 1d 
B. The Leaf. . . . ieee, sat. Ta NA, ae ME 1a Sets Ses hod 
1. Connection ee Leaf sah Stem i Bech. Aloe ds Hiatt 
2. Form and Structure of the Leaf. . . . 2. . 1 1 we ee ee 785 
C. The Root. . . . ; Miva bee Glog ete gh oo 
1. Connection bebaeen Root aiid Sih ea ee ee ee ae 
2. Structure of the Root . . 2 1 we ee ee ee ee BB 
D. Habit and Dimensions of the Plant. . . . ....... . +. 759 
ii. Heteronyiumdilimoides § gw 6 ee ww we Re ey FOO 
iii. On a Heterangium of uncertain species . . . . . 1 se ee es es ee 164 
III. Affinities of Lyginodendron and Heterangium . . 1 6 1 ee ee ee ee 068 
Pieplamationvot the: Blaise da a. Gog Re Wang ahi Ue Bs ele ek Blk Gam 
INTRODUCTION, 
The two genera, Lyginodendron and Heterangium, are among the most interesting, 
and at the same time the most puzzling, representatives of the Carboniferous Flora. 
Although, unfortunately, we are still without any satisfactory evidence as to the 
nature of the reproductive organs in either genus, yet the structure of all their vege- 
tative parts is preserved with such completeness and perfection as to enable us to 
show, that these fossils present a combination of characters such as exists in no group 
of plants now living. So long as the mode of reproduction is unknown, it will remain 
impossible to assign these genera definitively to their systematic position ; in the 
mean time, we can only weigh with due care such evidence as is afforded by their 
vegetative structure. This evidence, as we shall show, clearly indicates, so far as it 
goes, a position intermediate between Ferns and Cycads. 
At least two other fossil genera, Poroxylon, which was investigated by 
MM. Berrranv and Renavutt, and Protopitys, our present knowledge of which is 
chiefly due to Count Sotms-LAuBacn, appear to share this intermediate position.* 
Curiously enough, in these genera, also, the vegetative characters alone are known. 
The further consideration of affinities will be postponed to the end of the paper, and 
we will now go on at once to consider the organization of Lyginodendron, which, of 
our two genera, appears to stand the nearer to Cycadez, though many of its charac- 
ters are obviously Fern-like. 
* BerrranD et Renautt, “Recherches sur les Poroxylons,” ‘ Archives botaniques du Nord de la 
France,’ 1886. 
Soums-Lavsacu, “ Ueber die in den Kalksteinen des Kulm von Glitzisch-Falkenberg in Schlesien 
enthaltenen Structur-bietenden Pflanzenreste—II.,” ‘ Botanische Zeitung,’ 1893. 
