SEED-COLORATION 391 



this family, both for albuminous and exalbuminous seeds, 

 that in the pre-resting or so-called immature state green 

 embryos and green seed-coats go together. 



In this connection I come now to refer especially to the The colour- 

 behaviour of the embryos of albuminous seeds. The changes the embryos 

 in colour which the green embryos of full-sized unripe seeds QUS see^ n " 

 undergo when entering the resting stage, and subsequently 

 when germination begins, are well illustrated for leguminous 

 plants by Poinciana regia, Cassia fistula, and Bauhinia. These 

 seeds are similar in the general sense that the embryos, which 

 have large foliaceous cotyledons, are nearly as long and as broad 

 as the seed, and are placed between two slab-like masses of 

 albumen. When these seeds are here characterised as unripe 

 or immature, reference is made only to those seeds that have 

 reached the maximum size in the soft condition in the green 

 pod. In such seeds the embryos, being fully formed, are, as 

 shown in Chapter XIX, quite able to dispense with the rest- 

 ing stage altogether, and to proceed with their growth, or to 

 germinate, as we term it. But on account of the cutting 

 off of the fluid supplies and the drying of the pod, a resting 

 period is imposed upon them. It is this break in the continuity 

 of its life that is strikingly shown in the changes of the colora- 

 tion of the embryo. 



In this respect my remarks will be mainly confined to the as illus- 

 behaviour of the embryo of Poinciana regia, and I will make seeds of 



but a brief reference to those of the other two plants, since Pom 



regia. 



they behave in a similar manner. In a green semi-ligneous 

 pod of full size the seeds of Poinciana regia are pale green, 

 and possess soft, flexible coverings. The albumen is white 

 or colourless, and remains so during the subsequent stages. 

 The embryo has dark green cotyledons and a white caulicle 

 or stem ; whilst the pale green plumular bud, which is partly 

 expanded and stands 3 millimetres high, is far more suggestive 

 of a continuously growing plantlet than of an embryo that 

 is shortly to be compelled by the stress of circumstances to 

 enter the rest-period. When the pod begins to dry and to 



