IOWA ACADEMY OF SCIENCE 
109 
BEHAVIOR OP POLLEN TUBES IN RICHARDIA APRICANA. 
J3Y JAMES ELLIS GOW. 
During the past year the writer undertook an investigation of the morpho- 
logy of Richardia africana, (the ordinary Calla Lilly, otherwise known as Calla 
ethiopica, or Zantedeschia africana), with a view of discovering what might 
be found relative to its life history, and comparing its life history with that of 
other Aroids. In at least one respect the results w'ere curious and unexpected. 
In the greenhouse, pollination of Richardia is seldom accomplished except by 
artificial means. Unpollinated material was at first experimented with. In the 
younger blossoms, the ovule appears as a well defined nucellus, surrounded by 
one integument which is just beginning to develop. At this stage, the primary 
archesporial cell is prominent, lying in the middle of the nucellus-tip. It is 
larger than the surrounding cells, has a better-defined nucleus, and reacts 
differently to stains, being much more responsive to the Haematoxylin than are 
the surrounding cells, and taking Safranin or Gentian Violet much less diffusely, 
the staining of the former especially being largely limited to the chromatin, the 
network of which seems sharply defined from the first. This cell develops 
directly into the embryo-sac. 
Between the first appearance of the primary archesporial cell, and the final 
appearance of the embryo-sac, the ovule nearly doubles in size, the nucellus 
becoming much longer, and the integuments (which have now become two) 
lengthening out, and overlapping the tip of the nucellus. Some nucelli, at this 
stage, show a well-defined megaspore, and some show a well-defined 
embryo-sac, but most of them consist merely of a mass of perfectly sterile tissue, 
without differentiation of any sort. The ovary continues to swell for a time, 
and then begins to wither. The cells of the mature nucellus are large, thin- 
walled, and very much like the endosperm-tissue common in many of the Aroids, 
but of course are quite a different thing morphologically. 
The experiment of fertilization was tried about the middle of January. In 
the course of a week a few sections were made, but with negative results. Early 
in February it was observed that the ovaries were swelling rapidly and had 
reached about double their former size. Upon sectioning the material it was 
found that all parts of the ovule had grown; the nucellus having nearly doubled 
in length, and the integuments having kept pace with them. A very few showed 
indications of containing a badly disorganized embryo-sac, but most of the nucelli 
were, as before, perfectly sterile. Pollen tubes, however, had penetrated the 
carpel, and had in many cases approached the tip of the nucellus, and in at 
least one instance a tube had penetrated the tip of a perfectly sterile nucellus. 
The tubes were well preserved, stained well with the triple stain (haematoxylin- 
safranin-orange G), and showed the fertilizing cell and tube-nucleus well in 
many ways. There was very little shrinkage or distortion. Older material, 
investigated ten days later, showed a breaking down both of the pollen tubes 
and the sterile nucelli, but in a few cases the pollen tubes could still be seen 
penetrating the tips of the now partially disintegrating nucelli. 
