
730 THE AMERICAN NATURALIST. [Vor. XXXVI. 
According to that author the change is merely a gradual flat- 
tening of the petiole, accompanied by the reduction of parts 
more distal. The stage represented in his paper is explained 
in the following words: ** Wo es zu breiten Phyllodien mit nur 
einem Fiederpaar an der Spitze kommt, entsprach in den von 
mir gesehenen Fallen das Phyllodium einem nur oberseits 
geflügelten Blattstiel, das Fiederpaar dem untersten Fieder- 
paar eines Fiederblattes, Spindel und höhere Fiederpaare 
würden somit als abortirt anzusehen sein, Steht auf der 
Spitze eines Phyllodiums einmal ein zweipaariges Fiederrudi- 
ment, so pflegt die Spindel zwischen den beiden Fiederpaaren 
ungeflügelt zu bleiben ” (p. 568). 
Reinke is naturally giving only the results of his own obser- 
vations, yet one cannot but draw the inference that a certain 
law is at least suspected, czz., that only the petiole flattens in 
each case, and that at the same time the distal parts gradually 
cease to develop, until at last the stage is reached which this 
writer figures, after which the last pair of pinnz fails to develop, 
and the phyllode is complete. 
In the botanic garden of Harvard University there are two 
species of Acacia which show these transition stages in great 
abundance. They agree well in leaf characters with A. rubida 
and A. heterophylla, and will be discussed under these names, 
though full identification was not possible, owing to absence of 
flowers and fruit. Whether or not the determinations are 
right, the principle which they illustrate remains the same. 
Of both of these species the writer made a special examination 
during the spring of 1900, with a view to observing the different 
transition stages, their sequence and character. Upon re-read- 
ing Reinke's article in the summer of igor, and finding there 
certain statements which in a way did not correspond with his 
results, he repeated the examination and ran across more pecu- 
liar forms which tend rather to disprove than to confirm the 
existence of any law governing such changes. 
. The first thing which appeared from these two examinations 
was that the method of reduction of the more distal parts 
described by Reinke, though indeed frequent, is perhaps not 
the most common of all. Rather more often an equal decrease 
