518 Sir John Luhhock [May 21, 



of the seeds, long narrow seeds naturally in most instances producing 

 embryos with narrow cotyledons. The cases, however, which can be 

 so simply accounted for are comparatively few. Many plants with 

 narrow cotyledons have flattened and orbicular seeds. In such 

 species, however, the cotyledons lie transversely to the seed. An 

 interesting case is afforded by the pink family, where the jpink itself 

 has broad cotyledons, while the chickweed has narrow ones. In both 

 cases the seeds are flattened and orbicular, but in the pink the seed is 

 dorsally compressed, and the cotyledons lie in the broad axis of the 

 seed ; while in the chickweed seed is laterally flattened, and the coty- 

 ledons lie transversely to the seed. 



Another very interesting case which he gave is that of the genus 

 Galium, to which the common " cleavers " of our hedges belongs. 

 Here also we find some species with narrow, some with broad coty- 

 ledons ; but the contrast seems to be due to a very different cause. 

 Galium aparine has broad, Galium saccharatum narrow, cotyledons. 

 So far as the form of the seed is concerned there is no reason why the 

 cotyledons should not be much broader than they are. The explana- 

 tion may perhaps be found in the structure of the pericarp, which is 

 thick, tough, and corky. It is very impervious to water, and may be 

 advantageous to the embryo by resisting the attacks of drought and 

 of insects, and perhaps even if the seed be swallowed by a bird, by 

 protecting it from being digested. It does not split open and is too 

 tough to be torn by the embryo. The cotyledons therefore, if they 

 had widened as they might otherwise have done, would have found it 

 impossible to emerge from the seed. They evade the difliculty, how- 

 ever, by remaining narrow. On the other hand, in Galium aparine 

 the pericarp is much thinner and the embryo is able to tear it open. 

 In this case therefore the cotyledons can safely widen without endan- 

 gering their exit from the seed. The thick corky covering of Galium 

 saccharatum is doubtless much more impervious to water than the 

 comparatively thin test of Galium aparine. The latter species is a 

 native of our own Isles, while Galium saccharatum inhabits Algiers, 

 the hotter parts of France, &c. May not then perhaps, he suggested, 

 the thick corky envelope be adapted to enable it to withstand the 

 heat and drought. In this genus, as in many other plants, the 

 embryo occupies only a part of the seed, being surrounded by a store 

 of food or " perisperm." In many cases the embryo occupies the 

 whole seed, and the cotyledons must, therefore, in large seeds, either 

 be thrown into various folds, as in the beech, or be thick and fleshy 

 as in the bean or oak. The reasons for their numerous differences 

 open up an inexhaustible variety of interesting questions. Sir John 

 gave a great number of examples, which were rendered clearer by 

 means of numerous diagrams of seeds and seedlings. 



In conclusion, he said it might be asked whether the embryo con- 

 formed to the seed, or the seed to the embryo, and showed that, at 

 least as regards certain species, the former was the case ; while the 

 shape of the seed, again, might be shown to be influenced by consi- 



