SIR J. LUBBOCK — PHTTOBIOLOGICAL OBSEBYATIOXS. 401 



and irregular, several emhryos being contained in eacli seed, and 

 sometimes squeezed together iu the utmost confusion. 



In several otlier cases, among those which have been already 

 referred to, we can hardly doubt, I think, that the form of the 

 cotyledon has been affected by the seed and not vice versd. 



Let me in conclusion take one other illustration. The coty- 

 ledons of the Sycamore (fig. 9) are long^ narrow, and strap-like; 

 those of the Seech (fig- 13) are short, very broad, and fan-like. 

 Both species srt'e aperisper'mic, the embryo occupying the whole 

 interior of the seed. 



Now in the Sycamore the seed is more or less an oblate 

 spheroid, and the long ribbon-like cotyledons, being rolled up 

 into a ball, fit it closely, the inner cotyledon being often 

 somewhat shorter than the other. On the other hand, the nuts 

 of the Beech are more or less triangular : an arrangement like that 

 of the Sycamore would therefore be utterly unsuitable, as it 

 ■would necessarily leave great gaps. The cotyledons, however, 

 are folded up like a fan, but with more complication, and in such 

 a manner that they fit beautifully into the triangular nut. 



Can we, however, carry the argument one stage further ? Why 

 should the seed of the Sycamore be globular, and that of the 

 Beech triangular ? Is it clear that the cotyledons are consti- 

 tuted so as to suit the seed ? May it not be that it is the seed 

 which is adapted to the cotyledons? In answer to this we must 

 examine the fruit, aud we shall find that in both cases the cavit}' 

 of the fruit is approximately spherical. That of the Sycamore, 

 however, is comparatively small, say ^ inch in diameter, and 

 contains one seed, which exactly conforms to the cavity in which 

 it lies. In the Beech, on the contrary, the involucre is at least 

 twice the diameter, and contains from two to four fruits, which 

 consequently, in order to occupy the space, are compelled (to , 

 give a familiar illustration, like the segments of an orange) to 



form 



Th 



"^e see that it governs that of the seed, and that of the seed 

 again determines that of the cotyledons. But though the coty- 

 ledons often follow the form of the seed, this is not invariably 

 the case: other factors must also be taken into consideration; 



thro 



assume 



l-tNX. JOUBK. — BOTAXT, TOL. XXII. 2 L 



