1901.] NATURAL SCIENCES OF rHILADELPHIA. 317 



Ailanthus glandulosa (Tree of Heaven). 



Some interesting facts were brought out in the study of the leaves 

 of this species. Two kinds of leaves were met with, viz., trans- 

 formed or evolved leaves and arrested ones. In order properly to 

 understand the variations which have taken place, it is necessary 

 to refer to the seedling condition as a starting-point. According 

 to Lubbock,' the first leaves are compound, trifoliate, petiolate, 

 exstipulate; terminal leaflets acuminate, subacute, entire; lateral 

 ones slightly toothed, ultimately glabrescent, petiolate, light green, 

 alternately pinnate-nerved ; petioles ribbed or striated, covered 

 with short glandular hairs; the young leaves are also covered with 

 fine silky hairs near their edges. The normal fully developed 

 leaves are pinnate with an odd leaflet provided, as a rule, with 

 from 5 to 9 pairs of lateral leaflets. The youngest leaves of the 

 side or terminal branches are juvenile in form and of two kinds, 

 viz., undeveloped or arrested juveniles and seedhng juveniles. For 

 example, on one branch the lowest leaf is broadly lanceolate with 

 two small lobes with glandular apices on the upper entire margin; 

 the lower side has a larger glandular tipped lobe and an acute 

 sinus. This leaf is an arrested juvenile one, the primordium 

 growing out into the terminal leaflet before the formation of the 

 paired lateral ones. The second leaf of the same branch is pin- 

 nately trifoliate; the lateral j)aired leaflets asymmetric, cut away 

 obliquely on the lower margin and rounded on the upper, while the 

 terminal leaflet is broadly ovate, acuminate with a single basal, 

 glandular-tij^ped lobe on the upper margin. The other leaves of 

 this branch are pinnate with an odd leaflet provided with 5 to 6 

 pairs of lateral leaflets. The odd leaflet is lanceolate with two 

 glandular teeth on the lower margin and one on the upper. 



The second branch studied shows a somewhat similar condition 

 of affairs; the earliest formed leaf is more deeply lobed at the 

 base, each lobe with rather deep sinuses, the upper narrow sinus 

 cutting in almost to the midrib. The terminal leaflets of the 

 pinnate leaves are also narrowly lanceolate with glandular teeth 

 at the base. One leaf, however, is abruptly pinnate by the non- 

 development of the terminal odd leaflet. 



Two divergent types of leaves may be said thus to exist on the 

 same tree, one type of leaf being due to the arrestment cf the 



»1892, Lubbock, Seedlinc/s, I, p. 327. 



