PECULIAR STAGES OF FOLIAGE IN THE 
GENUS ACACIA. 
CARLETON E. PRESTON. 
Tute development of foliage leaves in general appears, from 
the results of investigations made thus far, to be a regular. 
increase in complexity, almost the same for the ontogeny of a 
single plant as for the race in historic development, as disclosed 
by fossil remains. As an especially good example may be men- 
tioned a series given by Jackson ('99) illustrative of the history, 
both phylogenetic and ontogenetic, of Liriodendron. For the 
genus Acacia, Reinke ('96) gives a very comprehensive review 
of the development based upon the seedling forms and com- 
parative study of the adults of the several subgenera, noting 
especially the phyllode-forming tendency. : 
As the first point which this paper aims to bring out deals 
with the bipinnate leaf and its development regardless of the 
phyllode, it may be well to call to mind the regular course of 
seedling leaf forms. The first leaf, after the cotyledons, is 
normally singly pinnate, with about four pairs of leaflets; 
the next is generally bipinnate, with but a single pair of pinnze ; 
further change is a mere addition of more such pairs along the 
main axis. A peculiar transition stage between the singly 
pinnate and the bipinnate is sometimes found in seedlings 
of A. leprosa Sieber when growing under cultivation. The 
shadow prints (Figs. 1 and 2) annexed show the nature of this 
peculiarity. The lower pair of leaflets only is replaced by a 
pair of strongly developed pinnz, while the rest of the axis 
runs on singly pinnate and rather weak in structure. As a 
rule, no such continuation of the main axis is to be found. 
In the case of Liriodendron, Jackson found some stages which 
could be regarded as progressive beyond the normal condition 
of the present species. Here the complexity was increased 
simply by augmentation of the number of lobes to the leaf. 
747, 
