aS ee | 
K.—BOTANY. 179 
parts of the stem. The epidermis and subjacent layers of the sporangial 
wall differ but slightly from the corresponding tissues of the branch, 
while the columella is continuous with the phloém, and resembles it 
in structure. The sporangium has no special stalk, and in some cases 
is forked, like the stem, having evidently been formed when the branch 
was in the act of dichotomy. 
In Rhynia the sporangia are better differentiated, but here also cases 
occur where the spore-bearing region differs little in structure from the 
branch which it terminates. In both genera the spore-containing organ 
is thus nothing but the more or less altered end of a branch, quite 
comparable to the stichidium, which is differentiated in some Red Sea- 
weeds as the receptacle of the tetraspores, while in other Alge of this 
group the tetraspores are produced in unaltered portions of the thallus. 
In Hornea the fertile branch-ending is less differentiated than in 
Rhynia, and we must be prepared to meet with related forms in which 
the spore-bearing region was not differentiated at all, except for the 
presence of the spores. 
Goebel taught that the sporangium was an organ sui generis, a 
special reproductive structure, which had never arisen from any vege- 
tative part of the plant.*° His view has been generally accepted, but, 
in the light of the conditions in Rhyniacez, appears to be no longer 
tenable. While the spores may still be described as organs sui generis, 
for there have always been reproductive cells since plants became multi- 
cellular, the sporangium proves to be really a portion of the vegetative 
stem or thallus, which has gradually become specialised as a receptacle 
for the spores. The sporangium thus turns out to be strictly homologous 
with a definite part of the vegetative body of the plant. In these 
remarks I am glad to find myself entirely in accord with the views of 
Kidston and Lang, as stated in their fourth memoir on the Rhynie 
plants. 
The recent work on the Early Devonian Flora has wide bearings. 
It has long been noticed that among the fossils of that period no typical 
Fern-fronds are found. Those remains which are most suggestive of 
Fern-like habit consist merely of a naked-branched rachis. It used 
to be assumed that the absence of a lamina might be explained by bad 
preservation. But, as Professor Halle points out, the chief reason for 
condemning the preservation as bad was the fact that a lamina was 
absent ! 
The evidence really seems to indicate that the so-called fronds of 
that age did not possess a leaf-blade. As Professor Halle says: ‘In 
the Lower Devonian, finally, we find frond-like structures bearing 
sporangia, but no fronds with developed lamine. One can hardly 
escape the conclusion that the ‘‘ modified ’’ fertile fronds may represent 
the primitive state in this case and that the flattened pinnules are a 
later development, as suggested by Professor Lignier.’? These naked 
6*Vergleichende Entwickelungsgeschichte der Pflanzenorgane.’ Schenk’s 
Handbuch der Botanik, Bd. III., Part I., p. 130, 1884. 
7T. G. Halle: Lower Devonian Plants, from Réragen, in Norway. Stock- 
holm, 1916, p. 38. 
