"I have just made a preliminary examination of the catkins from your hickory tree received last May, and it seems that the individual staminate flower of the catkin produces 4-5 undersized stamens, the anthers of which are devoid of either pollen or pollen-mother-cells. So far I have made only temporary preparations of the crushed anthers in stain but careful study of these mounts discloses no sign of pollen grains or mother cells, so we may tentatively conclude that no pollen is produced by the tree; in other words it is male-sterile. The stage at which degeneration of the pollen-forming tissue occurs in the anthers and its nature will have to be determined by means of a longer and more elaborate technique and I will let you know what we find as soon as the results are available. It may be that pollen-mother-cells are not even formed in the anthers; the small size of these structures and their more or less shriveled appearance lead me to believe that this may be the case.
"So far as I know there is no instance among nut species comparable to that outlined above. We have two or three cases of male sterility in chestnut but in these no stamens are formed in the individual staminate flower. In one of the hybrid walnuts that I reported on at the Hershey convention, imperfect pollen grains are formed in the anthers but the latter structures never open, so no pollen is shed.
"Bear in mind that the above report is preliminary and other angles may turn up when permanent mounts are available for study."
On December 14, 1943 I received a second, and final report from Dr. McKay from which I quote, as follows:
"Dear Mr. Weschcke:
The enclosed pencil sketches will give you an idea of the results obtained from sectioning four lots of material from the two samples of catkins that you sent, two lots from each sample. Since the sample collected May 25 at the time of catkin fall was old enough to contain mature pollen and showed only anthers of the two types described herewith I think we may safely conclude that the tree is male sterile because of the failure of the mother cells to function. It is odd that in some anthers the pollen-mother-cells develop (type 2) while in others they do not (type 1). For this we have no explanation; nor can we explain why the tree is male sterile. I am afraid these phenomena will remain a matter of conjecture for some time to come. Since sterilities of this and other sorts in most other plants are largely genetic, that is, controlled by one or more genes that are inherited in Mendelian fashion, it is likely that such is the case here. You and I will not live long enough, however, to grow the necessary number of generations of trees to clear up these matters.
"In the course of routine preparation of other material I plan to run up other lots from your samples, and I will let you know if anything different turns up. I believe we may safely conclude, however, that the results reported herewith are representative."
In further explanation, Dr. McKay submitted the drawings shown on page 57, and says:
"Four lots of material were sectioned, two from the collection of May 6 and two from that of May 25. Of these, two gave anthers of type one, and two of type two. More material will have to be sectioned before we know which type is predominant.
"The anthers of type one are greatly shriveled, and a band of deeply-staining collapsed cells apparently represents the remains of archesporial or pollen-forming tissue.