140 ON SEEDLINGS 



dons subsequent to germination. The following are instances 

 of broad cotyledons occurring in species scattered throughout 

 the order, namely : Matthiola ineana, Alyssum maritimum, 

 Hesperis nivea, Conringia perfoliata, Camelina sativa, Biscu- 

 tella didyma, Lepidium graminifolium, L. spinosum, Iberis 

 corifolia, and Chorispora tenella. A slight modification is 

 met with in ^Ethionema gracile and Iberis Lagascana, which 

 have unsymmetrical cotyledons, slightly oblique at the base, 

 and very much so in I. pectinata. It is probable that other 

 instances of the kind occur in Iberis and indeed in other 

 genera. The inequality at the base is due to the fact that 

 part of the space in the seed is occupied by the radicle 

 and petioles, which lie along one edge of the accumbent coty- 

 ledons. 



Emarginate cotyledons are almost as widely distributed 

 throughout the Order as those that are entire. The notch or 

 sinus is due to two totally different causes. The first type is 

 not owing to any peculiar conformation or structure of the 

 seed, the cotyledons being, as far as could be seen before 

 germination, entire. The notch in the seed-leaves is there- 

 fore due to the subsequent greater growth of the sides as com- 

 pared with the organic apex. Emarginate cotyledons occur 

 in Nasturtium sylvestre, Arabis Turczaninowii, Cardamine 

 hirsuta, C. graeca, Lunaria biennis, Cochlearia glastifolia, 

 Sisymbrium officinale, Bivonaea Saviana, and others. The 

 entire and emarginate state is shown in the figure of Sisym- 

 brium officinale (fig. 163). 



The second type of emarginate cotyledons occurs among 

 the Brassiceas and others, in which the cotyledons are con- 

 duplicate, as has been already mentioned in the Introduction 

 (see ante, p. 31). Brassica oleracea (fig. 169) may be 

 taken as a type. The cotyledons are emarginate with a 

 broad and moderately deep sinus, broader than long, un- 

 equal in size, trinerved at the base with alternate veins 

 upward, and the midrib forking below the apex ; the side 

 lobes are rounded and ascending. The inequality is due to 

 the arrangement in the seed, one cotyledon folding over 

 and completely embracing the other, which is necessarily 

 smaller, being in the centre of the sphere. The petiole 



