Notes . 
821 
NOTE ON THE PROTHALLUS OF LEPIDODENDRON VELTHEIM- 
IANUM. As the prothalli of Palaeozoic Lycopodineae are not as a rule well pre¬ 
served, we know exceedingly little about the gametophyte generation of the members 
of this gioup. In the case, however, of the megaspores of Lepidodendron Velthei- 
mianum , which occur in abundance in the Pettycur Limestone, the prothallus is never 
shed fiom the spore and occasionally its tissue is more or less perfectly preserved. 
In 1908 1 I drew attention to a specimen of this megaspore which was almost com¬ 
pletely preserved, and in the same year Dr. Scott figured another example. 2 The 
piothallus in my specimen showed a certain amount of differentiation into a cap of 
small-celled parenchyma at the apex of a larger-celled tissue. This cap was situated 
below the three ear-like projections of the spore coat which characterize this 
megaspore. As the spore coat did not show any trace of rupture (although the lines 
of rupture were indicated) I concluded that the specimen was immature. There 
were no traces of archegonia present in this example. 
The megaspore figured by Dr. Scott also shows traces of this differentiation, the 
smaller-celled parenchyma occurring where the spore wall is ruptured; but part of 
the prothallus seems to have been extruded from the spore. 
Recently I have obtained a specimen which, though less perfectly preserved than 
either of the above, throws considerable light on the development of the archegonia. 
The spore coat in this example also is ruptured (the splitting probably occurring 
between two adjacent ear-like projections), and below this gap there is a very distinct 
archegonium. The only cells of the prothallus which are preserved are round the 
archegonium, and they are similar in size to the cells of the cap in the examples 
mentioned above. In the accompanying figures, for which I am indebted to 
Mrs. Scott, this archegonium is exceedingly well shown. Fig. 1 a represents the 
whole spore with the external surface coated by knobbed hairs and the prothallus 
inside the spore coat. On the surface of this prothallus (which is shown more highly 
magnified in Fig. 1 b) a distinct papilla is seen. This papilla consists of the neck cells 
of the archegonium (n.c.) and immediately below the neck there is a dark mass (A) 
which probably represents the central cell. Separating the lower neck cells on the 
one side from those on the other is a narrow dark mass which in life would be 
the neck canal cell [n. c. c.). 
As far then as we can judge from this specimen, the development of the arche¬ 
gonium in Lepidodendron Veltheimianum was essentially similar to that in Selaginella. 
The archegonium mother-cell appears to have been one of the superficial prothallial cells 
which has divided into an upper and a lower cell, as in Selaginella. By the division of 
the upper cell into four and the subsequent division of each of these into three, the 
twelve neck cells have been produced. The whole neck consists of three tiers of four 
cells and there is no indication that it was ever bent over. On the right-hand side of 
Fig. 1 a there appear to be four neck cells in one row, but this is due no doubt to the 
wall between the two adjacent cells being oblique. The lower cell then appears to 
have divided into two, the upper forcing its way between the lower neck cells and 
1 Trans. Bot. Soc., Edinburgh, vol. xxiii, 1908. 
2 Scott, Studies in Fossil Botany, 2nd ed., Part I, p. 188, Fig. 77, London, 190S. 
3 K 
