LOCALIZED STAGES IX DEVELOPMENT. 105 



third leaf is a " character" leaf, having nearly or quite the full characters of the species. 

 It is five-lobed, whereas in some other seedlings the third leaf is trilobed; but this is 

 perhaps no more than might be expected in this protean species. The fourth leaf is also 

 five-lobed, but the lobation is not so pronounced as in the third. The fifth leaf, which is 

 very young, is slightly trilobed, resembling the second nepionic leaf. It is reasonable to 

 suppose that in further growth this young leaf would have taken on additional lobes like 

 the third and fourth nepionic leaves. For this and many other seedlings I am indebted 

 to Mrs. Robert T. Jackson. 



The English Ivy varies greatl}-, but selecting a branch, the fully grown leaf of which 

 is like the seedling figured, a comparison may be made. In such a branch (PI. 18, fig. 

 44), the fully developed leaf is five-lobed. Passing upward to the youngest leaves at 

 the tip of the branch, we find that the lobes become progressively reduced. The fifth 

 leaf has five lobes, but not strongly developed ; the sixth and seventh are simply trilobed. 

 The eighth leaf is weakly trilobed, .and bears considerable I'esemblance to the second 

 nepionic leaf of the seedling. While the leaves are very variable, it may be said that the 

 young leaves of new growths have fewer lobes or at least more weakly developed lobes 

 than the older leaves on the branches, thus making a more or less complete reversion to 

 the simple condition of the young. It is noteworthy that the simple trilobed leaves of 

 young seedlings and young leaves at the end of growing shoots (PI. 18, figs. 43, 44) 

 bear a close resemblance to Hedera cretacea Lesq., of the Cretaceous. 



Dahlia variabilis. The seedling of the common Dahlia {D. variabilis Desf.), has 

 simple, ovate leaves, succeeded by pinnatisect leaves. The typical leaves of the adult 

 have three, or more often five segments. Suckers from the crown frequently have 

 simple, ovate leaves at first, as in the seedling. On flowering shoots, especially late in 

 autumn, simple leaves are so common as almost to predominate. In these simple leaves 

 are seen distinct localized reversions to the simple condition characteristic of the young. 



Tecoma kadican.s. In the Trumpet Vine (Tecoma radicans Juss.) the seedling has 

 rounded cotyledons, distally deeply notched. The first nepionic leaves are simple, den- 

 tate, with petioles. There are two pairs of simple leaves, succeeded by compound, tri- 

 foliolate leaves. In later stages, additional leaflets appear, until the full character leaves 

 are attained. The distal leaflet of adult leaves resembles the simple nepionic leaf. In 

 suckers from the root, cases occur in which the first leaves are simple, as in the seedling. 

 Often, however, the first leaves developed in suckers are trifoliolate, the reversion being 

 more or less complete in different individuals. 



Fraxikus AMERICANA. The ashes present interesting features in development and 

 localized stages in development. In the development of the White Ash (Fra.rlnus ameri- 

 cana L.) the seedling (PI. 18, fig. 45) has oblong, obtuse cotyledons. The nepionic 



