BEHAVIOR OF THE POLLEN TUBE 101 
chin's contention, that the primitive behavior of the pollen-tube 
was entirely intercellular, is true. 
2. The conductive tissue of the style consists of: (I) very thin- 
walled cylindrical cells in the upper part and (2) thicker walled 
cells in the lower part. The latter pass from a cylindrical to an 
irregular isodiametric form in the fusion tissue, in which the 
middle lamella is evidently soft and yielding. 
3. A conductive tissue is here described which is morpholog- 
ically a part of the ovule, or, more exactly, a part of a peculiar 
secondary outgrowth which I have designated the strophiole. It 
takes two histological forms : (1) In Diodia Virginiana it is com- 
posed of cubical, mucilage secreting cells, with thickened outer 
walls, corresponding to analogous cells found in many plants on 
the placenta. (2) In Diodia teres and Richardsonia pilosa the 
homologous tissue is composed of columnar, thick-walled cells 
(the thickening being absent from their bases only) with a soft 
middle lamella. No outer mucilage layer is here found. 
In these plants we find a conductive tissue composed of elon- 
gate, regular cells, in which their longitudinal axes are placed at 
right angles to the intercellular path of the pollen tube for the 
direct passage of which this condition is mechanically less favor- 
able than in the kind of conductive tissue in which the longitudinal 
axes of the component cells are parallel to the path of the pollen 
tube. 
4. The pollen tube does not in general act unfavorably upon 
the cells with which it comes into contact. When however it 
does it may be referred to mechanical causes. This conclusion 
appears to accord with the observations of others. 
5. The pollen tube shows a tendency to branch where the 
cells are irregular and isodiametric, or where the long axis of the 
conductive tissue cells are placed at right angles to the course 
of the pollen tube. This behavior speaks against the view of 
Miyoshi: “Im Griffel werden die Pollenschlauche wesentlich me- 
chanisch zum Fruchtknoten gelenkt” (8). 
6. There remains an undetermined factor in the guidance of 
the pollen tube. We cannot tell how the same is able to find its 
way to the egg in the definite way in which it does. The pollen 
tube is negatively aérotropic, and is chemotropic, as shown by 
