,8,.. OUR KNOWLEDGE OF SEEDLINGS. 753 



forming minute, scarcely elevated green teeth at the junction of the 

 fleshy hypocotyl and stem. 



In some of the marsh species of Ranunculus the cotyledons are 

 narrow and elongated, like the leaves. 



Where the seed contains no endosperm but is filled by the em- 

 bryo, the shape of the cotyledon must often largely depend on the way 

 in which it is packed, and its relation to the leaves subsequently 

 produced will not be evident ; but if we compare cases where the 

 embryo is so embedded in endosperm as to be apparently uninfluenced 

 by the shape of the seeds, and where, moreover, the seed-coat splits 

 widely on germination, allowing a free exit, we may sometimes find 

 some rough resemblance in the relation between the seed-leaves and 

 those of the adult. 



Thus, in the Cistineae, where these conditions hold, two leading 

 types of cotyledons are represented by the two leading genera Cistus 

 and Helianthevmm ; in the former they are comparatively narrow, in 

 the latter broad, and the ultimate leaves, at any rate in the case of 

 the species considered, will be found to bear a similar relation, those 

 of Helianthemum being the broader. This relation may sometimes be 

 observed also, other conditions being similar, where the seeds are 

 exalbuminous. Thus, two species of Matthiola are described, in one 

 of which, M. incana (Fig. 3), the cotyledons, the primary and ultimate 

 leaves are respectively broader than in the other, M. bicornis (Fig. 4). 



Such relations are, however, quite exceptional, and the contrast 

 between the seed-leaf and the ultimate form is certainly striking. Some- 

 times the adult form is assumed abruptly, as in the cactus family above- 

 mentioned, and this may happen even when the leaf is a highly deve- 

 loped compound one, as in some Leguminosae, e.g., jEschynoviene aspera 

 (Fig. 5). Very often, however, in species with compound leaves, the 

 two following the cotyledons are simple and opposite, as in Indigofera 

 attstralis (Fig. 6), the scarlet-runner [Phaseolus vulgaris), Pueraria (Fig. 7), 

 and other Phaseoleae. Frequently we find a more or less perfect 

 gradation to the adult form, as in Ceratocephalus (Fig. 8) or Ranunculus 

 arvensis (Fig. 9). 



Where the cotyledons are thick and fleshy, serving merely as a 

 store-house of reserve material for the growing seedlings, and remain- 

 ing in the seeds usually beneath the ground, the first few leaves 

 are reduced to small scales, as in Sapindtis incequalis (Fig. 10). Green 

 assimilating leaves are unnecessary while the store in the seed is 

 inexhausted, and the whole energy of the seedling can be more 

 profitably spent in raising it as high as possible into the light and 

 air, and out of the influence of surrounding vegetation. 



In a few rare cases the cotyledons by growth after germination 

 do come to resemble the ordinary foliage leaves. The Onagrarieas 

 supply most of the examples. The cotyledon at first bears no relation 

 to the subsequent form, but a new growth takes place at its base, so 

 that the whole organ finally resembles in form and appearance the 



3B 



