96 ROBERT TRACY JACKSON ON 



sinuses, being quite close in form to leaves in late growth of seedlings, or regressive leaves 

 of adults (Fig. 13, leaf 1). In L'irlodendron gifjanteiini Lesq., from the Cretaceous, the leaf 

 is four-lobed, with av ell-developed sinuses, and resembles leaves of young trees, or four- 

 lobed leaves of adults (Fig. 1). 



Holm ('90) has questioned the validity of these fossil species, because variations 

 equivalent to them may be found in our modern species. His objection may be met by 

 the reasonable suji^aosition that, in fossilization, only the average leaves of the tree stand 

 any probable chance of preservation. Aberrant leaves, in virtue of their small number, 

 stand relatively a slight chance of preservation as fossil representatives of ancient floras. 



AiLANTHUS GL.WDULOSA. In AUanthiis glandulosa Desf. the seedling (PI. 16, 

 fig. 15) has broad, rounded cotyledons of leathery consistency. The first two nepionic 

 leaves are opposite, compound, composed of three leaflets each. The terminal leaflet is 

 lanceolate, the lateral leaflets have entire margins. Succeeding leaves are alternate in 

 arrangement. They are also trifoliolate, but soon more leaflets are added. A specimen 

 seven inches high has seven leaflets on the youngest or last added leaves. Part of the 

 leaflets of the two upper leaves of PI. 16, fig. 15, have already acquired slight notches, 

 wliich are a characteristic feature of adult leaves. According to Lubbock ('92) the first 

 nepionic leaves of Ailanthus glandidosa var. rubra are also trifoliolate. 



The adult Ailanthus glandidosa has very large compound leaves, imparipinnate, with 

 about 25-33 leaflets. The distal ends of the leaves closely resemble the first nepionic 

 leaves of seedlings, differing principally in the added marginal notches. In an adult tx'ee 

 in Cambridge, at a point where a branch had been broken, a weak late growth was thrown 

 out. In this growth all the leaves had few leaflets, and one leaf had only three ; therefore, 

 excepting for its marginal notches, repeating the characters of the first nepionic leaf of the 

 seedling. In all of these depauperate leaves the terminal and other leaflets were similar 

 to those seen at the ends of normal adult leaves. The reduction was in the suppression of 

 the proximal portion of the leaf, or that portion wdiich is formed last in the ontogenesis 

 of the leaf. 



This species suckers freely from the roots, suckers often appearing at a considerable 

 distance from the base of the trunk. Suckers at first usually have simple leaves (PL 16, 

 fig. 14), though occasionally the first leaves seen were trifoliolate. These simple leaves are 

 alternate, ovate, elongate, similar to, but relatively shorter than, the distal leaflet of the 

 leaves of seedlings. Succeeding the simple leaves are compound leaves, first ti'ifoliolate, later 

 with more leaflets, the leaves all being alternate in arrangement. It is a striking fact, 

 the only case so far seen, that the suckers are simpler, more primitive than the seedling. 

 Whereas the seedling starts with opposite trifoliolate nepionic leaves, the sucker begins 

 with alternate simple leaves. In the Ailanthus then we find nepionic characters repeated 

 in suckers and I'egressive leaves of feeble growths. 



