an archaic type of Seed from the Palaeozoic Rocks . 93 
exterior, whilst that of the allied seed, Conostoma oblongum , was provided 
with a long tube, constricted or articulated at its insertion, the possibility 
of the existence of a caducous or non-permanent structure in Physostoma 
cannot be absolutely dismissed. 
If the actual structural details are obscure, so, too, is the agent of 
transport. The quantity of pollen found in the pollen-chamber suggests 
an agency of greater precision than mere wind-dispersal, unless the collecting 
drop at the tip was much more persistent or the load of pollen brought by 
the wind far greater than is generally the case at the present day. The 
suspicion is difficult to resist that insects may have been attracted to these 
seeds in search of the mucilage or nectar or whatever it was that formed 
the drops. 1 In the contemporary flora the Pteridosperms must have been 
relatively important from this point of view, for the Angiosperms, with 
their superior attractions for insects, had not yet invaded the field. Still, 
even should this be conceded — that the ovules were visited for their drops — 
there would be little result unless the insects had the regular habit of 
frequenting the pollen-bearing organs, the Telangiums and Crossothecas, 
of which we know so little. Perhaps, when existing Cycads, Welwitschia y 
and other Gymnosperms have been more fully studied in respect of their 
relations to insects, it may become profitable to consider the pollination- 
methods of the Pteridosperms. The present discussion will have served its 
purpose if it lead to attention being directed to the living forms. 
6. The Pollen-grains and Spermatozoids. 
The pollen-grains of Physostoma are ellipsoidal in form, with average 
dimensions of 55 x 45 fx. They are the smallest sized 
pollen-grains met with in the four species of related 
seeds found as petrifactions in the Lancs- Yorkshire 
Coalfield. The dimensions of the others are as fol- 
lows : Lagenostoma Lomaxii , 70 x 55 fx ; Lageno stoma 
oroides y 70 x 55 fx ; Co no stoma oblongum y 73 x 55 fx. 
Many of the grains of Physostoma show distinct 
traces of an internal cellular reticulum which recalls 
that of the pollen of the French seed Stephano- 
spermum akenioides . 2 An example is represented in 
the accompanying Text-fig. 8. In view of the ob- 
servations to be described below, many or most of 
these internal cells, and especially the larger ones, 
probably produced each a spermatozoid. Whether 
the residuum of smaller cells (of which there is some indication) was 
prothallial in nature, must remain undecided. 
Text-fig. 8. Pollen- 
grain of Physostoma show- 
ing the internal cells. The 
dotted area is the exo- 
spore where it has not 
been ground away. The 
grain occurs in Mr. Wat- 
son’s specimen (Text-fig. 
6). x 480. 
1 The suggestion first came from Sir Joseph Hooker ; see Oliver and Scott, On Lagenostoma 
Lomaxii , Phil. Trans. B., vol. 197, p. 214 (footnote). 
2 Oliver, On Stephanospermum . Trans. Linn. Soc., 2nd Ser., Botany, vol. vi, PI. XLIV, Fig. 33. 
