Morphological Char oxters 219 



cells within the grain can be demonstrated ; sometimes we can even 

 see how the cell-walls broke down to emit the sperms, and quite 

 lately it is said that the sperms themselves have been recognised 1 . 

 In no case, however, is there as yet any satisfactory evidence for the 

 formation of a pollen-tube ; it is probable that in these early Seed- 

 plants the pollen-grains remained at about the evolutionary level 

 of the microspores in Pilularia or Selaginella, and discharged their 

 spermatozoids directly, leaving them to find their own way to the 

 female cells. It thus appears that there were once Spermophyta 

 without pollen-tubes. The pollen-tube method ultimately prevailed, 

 becoming a constant "morphological character," for no other 

 reason than because, under the new conditions, it provided a more 

 perfect mechanism for the accomplishment of the act of fertilisation. 

 We have still, in the Cycads and Ginkgo, the transitional case, where 

 the tube remains short, serves mainly as an anchor and water- 

 reservoir, but yet is able, by its slight growth, to give the spermato- 

 zoids a "lift" in the right direction. In other Seed-plants the sperms 

 are mere passengers, carried all the way by the pollen-tube ; this 

 fact has alone rendered the Angiospermous method of fertilisation 

 through a stigma possible. 



We may next take the seed itself— the very type of a morphological 

 character. Our fossil record does not go far enough back to tell us 

 the origin of the seed in the Cycadophyta and Pteridosperms (the 

 main line of its development) but some interesting sidelights may 

 be obtained from the Lycopod phylum. In two Palaeozoic genera, 

 as we have seen, seed-like organs are known to have been developed, 

 resembling true seeds in the presence of an integument and of a 

 single functional embryo-sac, as well as in some other points. We 

 will call these organs "seeds" for the sake of shortness. In one 

 genus (Lepidocarpon) the seeds were borne on a cone indistinguish- 

 able from that of the ordinary cryptogamic Lepidodendreae, the 

 typical Lycopods of the period, while the seed itself retained much 

 of the detailed structure of the sporangium of that family. In the 

 second genus, Miadesmia, the seed-bearing plant was herbaceous, 

 and much like a recent Selaginella 2 . The seeds of the two genera 

 are differently constructed, and evidently had an independent origin. 

 Here, then, we have seeds arising casually, as it were, at different 

 points among plants which otherwise retain all the characters of their 

 cryptogamic fellows; the seed is not yet a morphological character 

 of importance. To suppose that in these isolated cases the seed 



1 F. W. Oliver, "On Physostoma elegans, an archaic type of seed from the Palaeozoic 

 Rocks," Annals of Botany, January, 1909. See also the earlier papers there cited. 



2 See Margaret Benson, "Miadesmia membranacea, a new Palaeozoic Lycopod with a 

 seed-like structure," Phil. Trans. Royal Soc. Vol. 199, b. 1908. 



