AXIAL ABSCISSION IN IMPATIENS SULTANI 
49 
Apparently, the plant comes from the more shaded African rain 
forests,^ the specific name being in honor of the sultan of Zanzibar. 
Beginning with the accidental observation that some time after 
cutting back the plants, segments of internodes were found upon the 
soil beneath, we have made a considerable series of careful observations, 
embracing several hundreds of operations. Summarily stated these 
lead to the following conclusions: 
1. Young branches of /. Sultani which are severely injured by the 
attacks of greenhouse pests may be cut off from the main stem by a 
sharply marked abscission zone and fall from the plant. The same 
seems to be true of shoots which have been injured in some other 
manner. In some cases we have induced the abscission of a branch 
by passing an electric spark through the stem, but beyond a few pre- 
liminary experiments we have given little attention to this method. 
2. When a large plant is removed from a shaded room and trans- 
planted out of doors, abscission of a number of the smaller branches 
almost invariably occurs. The same is true if a large cutting is made 
and planted, without previous trimming, in a well-lighted spot. 
3. If an internode be cut across at almost any point between the 
nodes, the portion of that internode which remains will in the course of 
a few days fall from the plant. This is brought about by the formation 
of an abscission zone immediately above the axillary bud of the leaf 
of the preceding node. After the section of internode has fallen the 
surface left is generally very smooth — almost as smooth as a knife cut. 
Usually the cut is diagonal in direction, rather than transverse, begin- 
ning immediately above the axillary bud and extending downward 
and across the stem, so that a maximum amount of stem tissue is re- 
moved without injury to the bud. 
4. If the operation be made very close to the subtending node 
abscission may apparently in rare cases not occur, the cut surface 
simply drying up. It is always difficult, however, to be sure that 
there has not been formed a separation zone which removed only a 
thin layer of cells on the cut surface. This is undoubtedly what occurs 
in many instances. 
5. Almost invariably the abscission occurs above the first (most 
nearly terminal) node below the cut, but occasionally it may take 
^Engler. Sitzungsber. Kgl. Akad. Wiss. Berlin 16: 191-211. 1900; Just's Jahres- 
ber. 28^: 389. Among the plants investigated by Burgerstein /. Sultani, Ipomoea 
purpurea, and Tropaeolum Lobbianum were the only species which flowered well in 
the shade. 
