LOCALIZED STAGES IN DEVELOPMENT. 93 



Localized Stages ix Developmext in Plants. 



In many cases in the following pages simple stages in the development of seedlings 

 are described, often in considerable detail, bnt these are not to be confused with localized 

 stages in development which are compared with them. Sir John Lubbock's work on seed- 

 lings has been a great help and is frequently referred to. 



In the nomenclature of stages in development of animals, the term nepionic is applied 

 to stages innnediately succeeding the embryonic. The term has not been applied before 

 to plants, but as cotyledons are the last of the truly embryonic features, the immediately 

 succeeding growth is considered as the nepionic stage. 



In the higher plants the tij^ of the leaf is formed first, and usually growth ceases early 

 at that point, it being transformed into permanent tissue (Sachs, '75). Such being the 

 fact, it is evident that the proximal portion of the leaf is formed last. The tip of the leaf 

 should be the most primitive portion, and the proximal portion, usually at least, the most 

 specialized portion, as is shown to be the fact in many cases in the following pages. If a 

 leaf undergoes an arrested development from any cause, the distal tip at least will be 

 formed, and the proximal portion will fail to develop or will be modified in varying degrees. 

 In progressive evolution newly added characters will be likely to make their appearance at 

 the proximal end of tlie leaf. As a corollary, in regressive evolution, regression will tend 

 to be evinced by a dropping out of characters at the proximal end of the leaf. 



Aquilegia canadensis. In the seedling columbine, AquiUgia canadensis L. (PI. 16, 

 fig. 16), the cotyledons are broadly rounded, with long petioles and a slight emarginate 

 distal notch. The first nepionic leaf is trifoUolate, the median leaflet having two marked 

 notches, and each of the lateral leaflets one slighter notch on the lower side. Later 

 nepionic leaves are similar. In the adult (PI. 16, fig. 17) the leaf has three bi-anches. 

 The two lateral divisions are trifoliolate and repeat the form of the median division. The 

 terminal division is trifoliolate, like the whole nepionic leaf. The median leaflet has two 

 major clefts, comparable to the two indentation.s of the median leaflet of the nepionic leaf, 

 and the two lateral leaflets each have a major cleft on the lower side, comparable to the 

 notches of the lateral leaflets of the nepionic leaf. While the adult leaf has relatively 

 deeper notches and in addition has minor dentations, we may see, in the leading featui-es of 

 the terminal leaflet, a repetition of the characters of the Avhole nepionic leaf of the seedling. 



LiRiODENDRON TULiPiFERA. In the Tulip-tree {Liriodendron taUpifera L.) the seed- 

 ling (PL 16, figs. 8, 11) has simple lanceolate cotyledons. The first nepionic leaves ai-e 

 alternate, distally emarginately truncate, rounded for the rest of their outline. The angle 

 between the truncation and cui'ved sides in the first nepionic leaves is rounded, but in 



