70 ON SEEDLINGS 



in Cheiranthus and other Arabidese the pods are flattened dor- 

 sally and the cotyledons are accumbent in the broad way of 

 the seed (figs. 73 and 74), those of the Sisymbrieae, to which 

 Heliophila belongs, have (fig. 115, A and B) the cotyledons in- 

 cumbent, so that they lie across the seed, and it is consequently 

 an advantage that they should be linear. 



Similar cases occur in other Orders, as for instance in 

 Caryophyllacese and Solanaceae. 



CONCLUDING EBMARKS. 



The conditions under which the seedlings are grown 

 naturally exercise some influence on the form of the leaves. 

 For instance, in Mimulus luteus, if the seedlings have sufficient 

 room the first leaves are shortly stalked and deltoid, while the 

 primary nodes are but little developed ; on the contrary, if 

 they are more crowded, the internodes and petioles are longer 

 and the leaves are oval. 



In the Primrose we find an arrangement which almost 

 seems as if it were intended to give the seedling some power 

 of locomotion. The hypocotyl is sometimes horizontal, and 

 throws out strong adventitious roots, the upper part, how - 

 ever, becoming vertical as usual. 



As a general rule, the first buds produced by the seedlings 

 are in the axils of the leaves, or more rarely of the cotyledons. 

 In some species of Linaria, however, the hypocotyl itself throws 

 out one or more buds which develop into branches. The 

 advantage of this may be that, if the main shoot is cropped 

 or broken even down to the root, the plant is capable of 

 throwing up another stalk. 



We thus find an almost inexhaustible series of beautiful 

 adaptations to purpose. On the other hand, there are not 

 wanting cases in which it would seem that the adaptation is 

 not complete, or that a certain change, which has been of 

 superior importance, has involved a minor evil. 



The Oak, Beech, Nut, &c. afford us a very interesting 

 series of species. Fig. 117 represents a diagram of a Nut 

 with the parts somewhat separated from one another, so as to 

 show the relations more clearly. The mycropyle (m) is at the 



