518 EVOLUTION OF THE EUCALYPTS, 



takes place along the median vein, from petiole to apex. Each 

 folds transversely, thus, into two halves, and one half of each 

 cotyledon lies between the two halves of the other, the radicle 

 Ij^ing in the centre between the two innermost halves of each, 

 and at the lower pole of the seed. One half of each, con- 

 sequently, lies against the testa. The lobed portion at the 

 intero-lateral angle of each half serves to ensheath the radicle. 

 The apex of the seed is occupied by the two apices of the coty- 

 ledons. In germination, the radicle emerges from the lower pole, 

 and rupture of the testa then takes place along the keeled, dorsal 

 margin of the seed. We thus see that, in the embryo, each 

 cotyledon has an enveloping half, which lies against the testa, 

 and an enveloped half, which lies against the radicle. In the 

 cortpnbosa-type, these are usually symmetrical. Similar folding 

 occurs in the Angophoras. 



(^ii.) E. (jlobidus may be taken as the type of the moderately 

 emarginate cotyledon. Comparing it with the reniform coty- 

 ledon of E. corymhosa, we see that it is as if a deep slice had 

 been taken out of the apical portion of the latter, leaving only 

 the intero-lateral, lobed portion of each half, which, as we have 

 just seen, ensheaths the radicle. Folding still takes place along 

 the line of the central vein, which is now very short ; con- 

 sequently, instead of being folded transversely, the halves of the 

 cotyledons are now deflexed and convolute over the radicle. It 

 will thus be seen, that the radicle is still embraced by the lobed 

 portion of one-half of each cotyledon, the other half of each 

 lying against the testa. The apex of the seed, however, now 

 contains the two lines of fold, which, in E. corymhosa, are along 

 each lateral margin of the seed. They have, therefore, moved 

 up to the apex. In E. globulus and many similar species, the 

 enveloped half of each cotyledon is smaller than the enveloping, 

 hence causing the cotyledons to be asymmetrical; in the seedling, 

 each larger half being opposite each smaller. In E. rtiaryinata, 

 with its large, slightly emarginate, obcordate, asymmetrical 

 cotyledons, the folding is transverse, the smaller half of each 

 cotyledon being enveloped within the doubled-over other coty- 

 ledon. Though the base is cuneate, in the embryo the lateral 



