EVOLUTION OF SEED-PLANTS 109 



details of their structure. The seed itself, pro- 

 tected by the cupule or husk, consists essen- 

 tially of a central body or nucellus, enclosed in 

 a seed-coat; these two parts are closely united 

 together except at the top. It will be remem- 

 bered that in modern Cycads and in the Maiden- 

 hair-tree there is a hollow chamber in the apex 

 of the nucellus serving to catch the pollen-grains. 

 The same arrangement is present in the seed of 

 Lyginodendron, and pollen is still found in the 

 pollen -chamber; the latter, however, is less 

 simple than in living Cycads, for a column of 

 tissue rises up in the middle of the chamber, 

 leaving only a narrow space round it for the 

 reception of the pollen (see fig. 13, pc). It is 

 interesting to find that the mouth of the pollen- 

 chamber projected a little through the micropyle, 

 so that it received the pollen directly, instead 

 of the grains having to traverse the micropyle 

 first. The seed-coat was supplied with a number 

 of vascular strands, and had a complicated sys- 

 tem of water-reservoirs in its upper part; they 

 may have provided the water necessary for the 

 purpose of fertilisation, if, as is probable, these 

 plants were like Cycads in producing swimming 

 sperms. 



We do not know exactly how the seeds were 

 borne in Lyginodendron oldhamium, except that 

 the seed-stalk was evidently part of a leaf, as is 



