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80 SIR J. LUBBOCK—PHYTOBIOLOGICAL OBSERVATIONS. 
is greater than their thickness. It follows that if they had been 
arranged as in the other species, they would not have had room 
to develop themselves. The difference of position is therefore 
explained by the fact that in P. media the width of the cotyle- 
dons is greater than the thickness; while in P. lanceolata &c., on i 
the contrary, the thickness of the two cotyledons, taken together, 
is greater than their breadth. 
The normal arrangement of an embryo in the seed is to have 
the faces of the cotyledons turned to the placenta. There are, 
however, not a few cases in which, as in these species of Plantago, 
the cotyledons have their edges to the placenta. When this is the 
case, it may be suggested as possible that the position is due 
to the fact of the seeds being more or less, in some cases very 
much, flattened; and that the embryo is twisted round at right 
angles to its normal position, so that the cotyledons may lie | 
in the broad way of the seed, as in Ailanthus, Euonymus, Pas- | 
siflora, Linum, Fraxinus, Diospyros, Heliotropium, and many | 
Crucifers, Leguminose, and Rosaceæ. ` 
On the other hand, in the case of Olaytonia this explanation 
will not apply. There would appear no reason, so far as the seed 
is concerned, why the cotyledons should not lie in the usual 
position. 
It has. occurred to me whether the arrangement of the coty- 
ledons may have reference to their exit from the seed. If we 
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Fig. 164. Fig. 165. 
Fig. 164. Claytonia perfoliata. Transverse section of seed. x 15. 
Fig. 165. Ditto. Seedling. x 6. 
examine a germinating seedling of Claytonia, we shall see that 
the testa splits vertically from the micropyle, and the cotyle- 
dons from their position, when they separate, act with greater 
