Painstaking Repair Begins on Microscope Slides from the Wood Anatomy Lab

By Michael Wiemann, Botanist, and Richard Kleiber Soares, Biologist, Forest Products Laboratory

The wood anatomy unit of the Forest Products Laboratory began its work in June of 1910 with the arrival of Eloise Gerry, the first woman scientist in the Forest Service. Gerry was hired to prepare and photograph microscope slides for wood anatomical study. This was a problem, because at the time the Lab didn’t have any wood samples!

This ad placed by the Lab for a “xylotomist,” or person who prepares microscope slides to examine woods, assumed that the candidate who got the job would be a man.

Gerry began to assemble a collection through donations from other institutions, primarily duplicates from Yale University’s wood collection. “Xylotomist” Arthur Koehler, famous for his work in the Lindbergh kidnapping trial, joined the wood anatomy staff in 1914 and brought with him a small wood collection. In 1945, when B.F. “Kuky” Kukachka was hired from his forestry teaching position at Louisiana State University, he began reorganizing the 11,000 samples in the Forest Products Laboratory wood collection.

Eloise Gerry at work at the Forest Products Laboratory

The number of samples increased gradually, then substantially with the addition of 55,000 wood samples (plus microscope slides) from Yale University in 1969, then again two years later with 8,000 more wood samples from the Chicago Field Museum. More than 7,000 prepared slides were donated by Duke University in 2007.

In addition to its 100,000 blocks representing more than 15,000 woody species from around the world, the wood collection of the Forest Products Laboratory now has 50,000 microscope slides of thin sections from these species. These slides were meticulously prepared by Lab personnel or were obtained through exchange or donation. Because it does not require a great deal more effort to prepare multiple slides than to prepare only one, many institutions exchange slides.

Restoration of slides began in April 2022 by Research Specialist Richard Kleiber Soares with funding from the Forest Service International Programs.

The samples prepared at the Forest Products Lab were typically used for wood anatomy research. One of the largest of these studies was wood anatomist B.F. Kukachka’s 1970s and 1980s work on the difficult pantropical genera of the Sapotaceae, a family of flowering plants that includes evergreen trees. This study was challenging not only because of its taxonomic complexity, but especially because the woods are “refractory,” meaning it is very difficult to prepare thin sections from them. Other studies focused on commercially important species whose separation from look-alikes is important to avoid inadvertent (or sometimes deliberate) misidentifications.

An unfortunate characteristic of one of the mounting media widely used in the preparation of microscope slides is its tendency to crystallize with age, resulting in partial or total obliteration of microscopic features. These slides must be cleaned up and remounted, a procedure requiring great care, patience, and skill. Remounting requires soaking a slide in xylene or an equivalent solvent to loosen the coverslip and sections, then carefully placing the freed sections onto a new glass slide with new mounting media.

Mounted Dalbergia sections (in crystallized medium) stored in a slide holder.

A recent survey of the slides in the Lab collection found that about one-third of them are unusable due to crystallization. The Dalbergia slides shown in the slide holder pictured below are examples of crystallization. Restoration of these and other slides began in April 2022 by Richard Kleiber Soares with funding from the Forest Service International Programs. Photographs from the slides of the two species show that the presence of crystallized mounting media can obscure the quality of the underlying sections. The cross-sections were excessively thick and had radial splits. However, the anatomical characters – such as the tangential bands of parenchyma in D. mammosa and the presence and absence of gum in both species – become evident after remounting.

Dalbergia mammosa (top) and Dalbergia lineata (bottom).

The photos below show a block of Bumelia lanuginosa with a “sectioning cube” removed; a slide prepared from it shows crystallization in progress, and a slide with the restored and remounted wood sections awaits proper labelling.  ‘Proj. I BWCw’ on the slide means that it came from the Brown Wood Collection at the College of Environmental Science and Forestry at Syracuse, the lead institution of Project I, in which various agencies cooperated from 1933 to 1953 in the collection of 800 vouchered wood samples from throughout the United States and Canada.

The photos of the block and two slides of Bumelia
The above photos of cross-sections (top four) and tangential sections (bottom four) show low and high magnification of Bumelia lanuginosa. Although the vessels and rays can be barely distinguished in the crystallized media (left), the remounted slides (right) clearly show that the wood is ring-porous, the latewood vessels and vascular tracheids are in dendritic pattern, apotracheal parenchyma is abundant, and the rays are two to three cells wide and heterogeneous