APPENDIX 487 



In Primula veris the placental axis in the living fruit is a fleshy 

 pointed dome which loses about 85 per cent, of its weight as the fruit 

 dries ; but owing to the presence of sugar it is hygroscopic and a little 

 sticky in the dried shrunken state. 



In Swietenia Mahogani^ where the fruit belongs to the woody- 

 capsule type, the axis or columella, though ligneous in appearance in 

 the living fruit, loses about 72 per cent, of its weight in drying, though 

 retaining its original regular prismatic form. 



NOTE 1 8 ( P . 395). 



On the colour of embryos. 



THE following additional remarks on the colouring of embryos may 

 serve to supplement the results given in Chapter XVII. As respecting 

 this feature of the embryo in resting seeds, which is the point to which 

 systematists generally restrict themselves, one may quote from Mrs 

 Hooker's translation of the System of Botany of Le Maout and Decaisne, 

 where it states (p. in) that "the colour of the embryo varies ; it is 

 white in most plants, yellow in some Cruciferae, blue in Salpiglossis y 

 green in the Spindle tree and Maples, and pink in Thalia.'''' 



The coloration of the embryo is apparently constant enough to 

 rank at times as one of the ordinal characters. It is noteworthy that 

 of the five orders mentioned in the above-quoted work as possessing 

 resting seeds with green embryos or green cotyledons, Zygophylleae, 

 Aurantiaceas, Rhamneae, Aceraceae, and Meliantheae, all belong to 

 the Discifloral series of the Polypetala j and although it does not seem 

 to be a frequent character with the Celastrineae, referred to the same 

 series, Euonymus^ which belongs to this order, possesses seeds with a green 

 embryo. The embryos in the orders above-named have often large, 

 flat, foliaceous cotyledons, and occupy most of the length and breadth 

 of the seed-cavity ; but in Melianthus the green embryo is very small, 

 lying in the midst of a copious albumen. 



NOTE 19 ( P . 453). 

 On the retrogression of plants under conditions of stress. 



As bearing on the retrogression of plants under conditions of stress, 

 one may recall Lord Avebury's remark on the frequency of small leaves 

 reduced to scales in seedlings with subterranean cotyledons, rudiments 



