1903.] on the Origin of Seed-hearing Plants. 337 



If the microspores could be brought to the megaspores while the 

 latter were still attached to the parent plant, much greater certainty 

 of their union would be gained, for adaptations would now become 

 possible for catching the small spores and retaining them in position. 

 Some of the Cryptogams now living have got as far as this ; the 

 work of an American lady, Miss Lyon, has shown that in some species 

 of Selaginella the microspores and megaspores meet and the sperma- 

 tozoids are discharged within the sporangium ; fertilisation is effected, 

 and even an embryo may develop before the megaspore is shed. In 

 this last respect these Selaginellas go beyond the Seed-plants of the 

 Palaeozoic period, as we shall presently see. 



The first advantage, then, to be secured, was the occurrence of 

 fertilisation, or rather the bringing together of the two kinds of spore 

 on the parent plant. This is one of the constant characteristics of 

 the seed-bearing plants ; the process is spoken of as pollination^ for 

 what we call the pollen-grains are nothing but the microspores of the 

 Spermophyta. 



We will now see Ijow the process actually goes on in some of the 

 simpler Seed-plants of the present day. 



The Seed-plants, as is well known, are divided into two great 

 classes : the Angiosperms, in which the seeds are inclosed in a seed- 

 vessel ; and the Gymnosperms, in which they are exposed. In the 

 former, fertilisation is effected by the growth of the pollen-tube 

 through the tissues of the young seed-vessel ; in the Gymnosperms 

 the pollen falls directly on to the young seed or ovule, and the pollen- 

 tube has only a short way to grow before reaching the egg-cell. 



The Angiosperms (Monocotyledons and Dicotyledons) include 

 practically all our familiar Flowering plants, but with them we are 

 not concerned this evening. The question of the origin of Angio- 

 sperms is one of the great unsolved problems of Botany, but it does 

 not immediately touch our present subject. It is to the simpler 

 Seed-plants — the Gymnosperms — that we must turn for light on the 

 origin of the Seed-plants as a whole. The Gymnosperms are 

 enormously the more ancient of the two classes, extending back 

 through the whole of the Carboniferous period into the Devonian, 

 while the Angiosperms, so far as we know, only appeared quite late 

 in the Mesozoic period. 



The mo>t familiar of the Gymnosi3erms — the Coniferae or cone- 

 bearing trees — are themselves too advanced on the seed-bearing line 

 for our purpose ; we will concentrate our attention on a family, 

 which of all living Flowering plants stands nearest to the Crypto- 

 gams, namely the Cycads. This group, not very well known to the 

 non-botanist, but of which a splendid collection will be found in the 

 Palm-house at Kew, is now a small one, including 9 genera and about 

 70 species distributed over the tropical and sub-tropical regions of 

 both the old and new worlds. In habit these plants, which may rise 

 to the stature of small trees, bear some superficial resemblance to 

 Palms ; the agreement with Ferns is however much more striking. 



