108 Sir John Lubbock [April 25, 



Lobed Cotyledons. 



The great majority of cotyledons are entire, but some are more or 

 less lobed. For instance, those of the mallow are broadly ovate, 

 minutely emarginate, cordate at the base, and three-lobed or angled 

 towards the apex, with three veins, each running into one of the 

 lobes. 



The embryo is green, curved, and occupies a great part of the 

 seed. The cotyledons are ajDplied face to face ; then, as growth con- 

 tinues, the tip becomes curved and depressed into a median longi- 

 tudinal furrow, the fold of the one lying in that of the other. 



[Sir John then showed by diagrams and paper cuttings how the 

 emargination arises, but it cannot be made clear without illustra- 

 tions.] 



The cotyledons of the Lime (Tilia) are very peculiar. They are 

 deeply five-lobed, the central lobe being the longest ; so that they 

 are roughly shaped like a hand. The seed is an oblate spheroid, re- 

 sembling an orange in form, and the embryo is embedded in semi- 

 transparent albumen. 



The embryo is at first straight ; the radicle is stout and obtuse ; 

 the cotyledons ovate-obtuse, plano-convex, fleshy, pale green, and 

 applied face to face. They grow, however, considerably, and when they 

 meet the wall of the seed, they curve round it, following the general 

 outline of the seed. If any one will take a common tea-cup and try 

 to place in it a sheet of paper, the paper will, of course, be thrown 

 into ridges. If these ridges be removed and so much left as will lie 

 smoothly inside the cup, it will be found that the paper has been cut 

 into lobes more or less resembling those of the cotyledons of the 

 Lime. Or if, conversely, a piece of paper be cut into lobes resembling 

 those of the cotyledons, it will be found that the paper will fit the 

 concavity of the cup. The case is almost like that of our own hand, 

 which can be opened and closed conveniently owing to the division 

 of the five finf^ers. 



Unequal Cotyledons. 



In most cases the two cotyledons are eipal, but there are several 

 cases in which one of them is larger than the other. This had not 

 escaped the attention of Darwin, who attributed the diflerence to the 

 fact " of a store of nutriment being laid up in some other part, as in 

 this hypocotyl, or one of the cotyledons." i confess that I do not 

 quite see how this aifords any explanation of the fact. The sugges- 

 tion I have thrown out is that the difference is due to the relative 

 position of the two cotyledons in the seed, which in some cases 

 favours one of them at the expense of the other. Thus in the mustard 

 they are unequal, and, as we have already seen, they are folded up, 

 one inside the other. The outer one, therefore, has more space, and 



