212 BOTANICAL GAZETTE [SEPTEMBER 
always divided; and that the entire leaves were of later growth. 
From further experiments he obtained the following data. All 
stems, regardless of external conditions, produced the water type in 
the autumn. Stems from which the vegetative points were 
removed in June threw out side branches with the water type of 
leaf, while normal plants under the same external conditions were 
producing the land type. In summer all plants, whether in water 
or air, developed the aerial form of leaf. Also, at the time of 
flowering only entire leaves were found. The change from the 
water to the land type took place earlier on strongly growing than 
on weak stems. 
From his experimental results Burns concluded that there are 
two forms of leaves, an adult and a juvenile, and that the produc- 
tion of these is not controlled by any one or more definite factors of 
the environment, such as light, moisture, temperature, etc. But 
under favorable vegetative conditions the adult form, the entire 
leaf, is produced, while under unfavorable the juvenile divided leaf 
is developed. Further, a reversion to the primitive or divided type | 
may be associated with unsuitable vegetative conditions. 
GOEBEL (3) experimented for several years with plants that 
exhibited the phenomenon of heterophylly, and his views fully con- 
firm those of Burns. He summarizes his conclusions concerning 
Proserpinaca as follows: 
Es ist klar, dass die Wasserumgebung nicht die Ursache der Blatteilung ist. 
Ebensowenig hingt sie ab vom Licht, der Temperatur, dem Gasgehalt des 
Wassers und dem Kontaktreiz als Solchem. Die einzige Folgerung, die sich 
aus meinen Versuchen ableiten lasst, scheint die zu sein, dass Proserpinaca 
palustris zwei Formen hat, eine “ Folgeform” und eine “Jugendform.” Unter 
guten vegetativen Bedingungen hat sie das Bestreben, die Folgeform mit den 
ganzen Blattern, Bliite und Frucht hervorzubringen, unter ungiinstigen Vege- 
tationsbedingungen hat die Pflanze das Bestreben, die Jugendform mit dem 
geteilten Blatt zu bilden. 
In view of the satisfactory results obtained from investigations 
on such morphological features, it seems entirely reasonable to hope 
that the anatomical aberrations occurring in galls may be capable 
of explanation by pursuing similar lines of inquiry and by making 
use of the anatomical principles unfolded by Scorr, JerFrRey, and 
others in recent years. Several of these aberrations have been 
