Texas Journal of Microscopy - Texas Society for Microscopy

Figure 13. HJA watering yucca seedlings in the Botany Greenhouse on
the roof of the Life Science Building in 1957. Photo by Jean Arnott.
of instant communication have greatly diminished that aspect
of botany. However, now as then, one’s major professor can still
make or break any student—the choice of a professor is not just
important, it is critical!
Much of my work on yucca was self-guided. I knew the general
direction I wanted to go and Foster was not one to look over your
shoulder. From time to time I would show Foster what I had been
doing, especially if it was exceptional. Mostly, I went on my own
way pushing the yucca research boundaries in various ways. I
raised seedlings in the Botany Greenhouse on the roof of Life
Science Building (Fig. 13). During that time, however, I did some
other research as the opportunity offered itself. I will describe two
cases to illustrate the point. I have already mentioned Cordyline
observations.
By my third year, I was working as Foster’s teaching Assistant
in both Plant Anatomy and Plant Morphology. On occasion, Foster
and I would go together to lunch at The True Blue Cafeteria, which
was in “downtown” Berkeley. The journey involved walking down
from the Life Science Building, through the grove of gigantic
Eucalyptus trees, along Strawberry Creek and then out into the
city and to the cafeteria; a total distance of ca. 0.3 miles. In those
days, there was no urgency and we would walk along admiring
what ever we came upon. Near the lower edge of the Eucalyptus
grove, there was a large Ginkgo biloba tree. On one of these “True
Blue” occasions, I collected a few leaves from under this ginkgo.
One of the leaves was especially interesting as it had two odd side
lobes (Fig 14).
At that time, I was involved in a major “side project” of clearing
plant material. Clearing is a process that uses chemicals (5% NaOH
and saturated chloral hydrate) to remove pigments in plant parts so
that their internal structure is exposed. Leaves, stems and flowers,
often taken from herbarium sheets (with permission) and personal
samples were cleared routinely; the many preparations were to be
a central part of my projected teaching career. Routinely, I decided
to clear that odd shaped ginkgo leaf.
In all the courses I had taken, including Foster’s, and in my study
of the literature, people stated categorically that Ginkgo had open
dichotomous venation; the veins branched but they did not fuse.
With that background, I was shocked to find two vein anastomoses
(fusions) in this odd leaf (Fig 14). I hastened to show it to Foster
and he was, quite literally, astounded! No one had ever reported
anastomoses in the veins of ginkgo. This simple discovery started
me on a ten-year investigation of venation in Ginkgo biloba and
other plants.
In the beginning, it was the venation of ginkgo, but soon
branched out to Ranunculus, Lemna and other genera. While
still in Berkeley I found out that Ginkgo biloba leaves have four
70 Tex. J. Micros. 37:2, 2006
Figure 14. Cleared “True Blue” leaf of Ginkgo biloba. Note the small
“ears” on each side of the lamina. Arrows point to anastomoses. With
permission, from Arnott H, J. Anastomoses in the venation of Ginkgo
biloba. Amer. J. Bot. 46:405-411.
different types of anastomoses; some involving one vein (types
A and B) and others involving two veins (type C and D) (Fig. 15).
Somewhat later, I found out that the four types of anastomoses are
not distributed at random in the leaves of long shoots. That is, the
type of anastomoses produced in ginkgo long shoot leaves is under
physiological control. Since Ginkgo had been long considered a
prototype for a primitive stage in leaf evolution these anastomoses
were of importance when considering the potential evolutionary
development of higher plant leaves.
Figure 15. Four types of anastomoses found in the leaves
of Ginkgo biloba. With permission from Arnott, H. J.
Anastomoses in the venation of Ginkgo biloba. Amer. J.
Bot. 46:405-411..
A second avenue of research also had its origin from clearing
leaves. I cleared the leaves of several species of ferns, including
Botrychium. Pieces of leaves were detached from herbarium sheets
(with permission). In a single species of Botrychium, I found very
unusual cells in the leaf mesophyll and along veins. Each cell
looked like it had a series of washers distributed along the cell. The