From Plant Press, Vol. 22, No. 3, July 2019.
By Julia Beros
Paul Sidney Conger made only one concession to using the Scanning Electron Microscope. That is, only once were the habits of Conger interrupted by the forces of change. For a career that spanned decades in the field of microscopy, Conger’s steady work was technical, meticulous, and though only visible under the lens of a microscope, monumental. After assisting Albert Mann at the Carnegie Institution for Science in his study of diatoms (1922-1935), he moved onto the USDA, which segued him to his career at the Smithsonian Institution (though his associated library material did not make the same institutional transition and remains with the USDA, much to Conger’s chagrin). Conger was named honorary custodian of diatoms, 1935-1943; then associate curator, 1944-1966; and botanist emeritus of cryptogams, 1967-1979. In a recent conversation with Harold Robinson the story of Conger’s contributions to the Smithsonian, microscopy, and diatoms sparked a long query into the quirks and legacy of Mr. Conger.
Revealing whole worlds to our human eyeballs, new images for neural pathways to decode and translate, the mystifying imagery of the microscopic world is nothing short of something unbound and celestial. Universes that exist under the guise of our human habitual. For Conger this universe was his second home. Known for mounting material on a slide with tight precision, he was able to manipulate indiscernible material with great accuracy. He was a mechanic of fine hand skills, using pieces of threads to slice or angle material, to mount and affix even the tiniest sliver of a specimen so that it would willingly reveal its hidden structures beneath the scope. He was a gifted technician, even in his early eighties.
In Conger’s day there were two methods of mounting diatoms: smearing them on a slide and recording the positions on the microscope setting, which meant the microscope was commandeered for the entirety of the time needed to study the material (i.e. indefinitely). Then there was Conger’s way; mounting the selected diatom on the center of the slide (sometimes a row of diatoms), and marking the position on the slide by surrounding it with the girdle removed from a large discoid diatom (ever resourceful), so that his subject was findable without coordinates. Many of his innovative ideas came from testing out new methods that he read about in one of his favorite magazines, Popular Mechanics.
Single celled alga with rigid silica shells, diatoms, were the focus of most of Conger’s microscopy endeavors. Too small to see, they exist en masse floating in oceans, rivers, lakes, the water; all one need do is dip a rope into the water and a “party-mix” of diatoms will eagerly attach. Viewed under high powered light microscopes, their great variety in structure and patterning are reminiscent of tiny jewels, pocket lint, or miniature plastic figurines. Many diatomists made great artworks under the microscope, creating mosaics from these tiny alga, and Conger even kept a collection of slides with these microscopic realist “paintings,” one even depicting a man with a cane on a leisurely stroll past a house.
One species, Baccillaria paradoxa, was of particular interest to Conger and his colleague Robinson. A colonial diatom in “peculiar arrangement” the single cells lay flat atop each other sliding laterally across their bodies, much like the arrangement of a fold-out ruler, without ever disconnecting at the tip. Most diatoms move against water, but in this case they move against each other in their colony. Perhaps they exchanged a bit of protoplasm in the 1/10 of the diatom that always remained connected to the adjacent cells. In the hope to discover the mechanism of communication and movement among the diatoms, Robinson convinced Conger that the Scanning Electron Microscope (SEM) would help them understand this curious organization. “The advent of the SEM had one great advantage. Previously the limited depth of focus in microscopic images made full views of objects like diatoms impossible,” Robinson recalls, “Conger would use double exposures, one to record the surface of the valve, and second to record the outline. This resulted in an unwelcome halo-effect. SEM had a greater depth of focus, and a whole diatom or pollen grain could be seen in clear focus.” The SEM shoots a focused beam of electrons back and forth that disperse throughout the microscope chamber and reconstructs these points electronically, much like a TV picture.
Conger was not the type to be rushed or corralled, even when it was time to move from the Smithsonian Tower Castle to the Natural History Museum he made special arrangements to take his time. On the second floor of the old south tower, two floors below the cryptogamic collection, and one floor below the old departmental library with the tile mosaic of the Smithsonian seal, Conger had a large work-space rarely visited by others in the department. Displaced from his oasis, he was sent to the West Wing of the Natural History Museum. Carrying his belongings over one by one in paper bags, a crusty old bottle of ether casually accompanying him across the National Mall (later attracting the attention of the bomb squad, for fear that it had crystalized into an explosive compound), the move began in 1965. Conger never quite felt settled in his new smaller office. Not one to be rushed into using a different tool either, Conger finally prepared his favorite diatom for the SEM. Using a thread powdered with crystals, he sliced the material in order to get a detailed interior look.
“I am not pleased with the views we have here,” mumbles Robinson as he goes over the stack of photos that were tucked away in his office in a trove of unpacked envelopes and parcels. Eerily unfamiliar, the images they captured of B. paradoxa are certainly humble in comparison with the false-color images of today’s microscopists. A diatom of 5 microns long, Conger was able to prop it up with a thread and make a cross section of the valves, exposing the raphe (where the streaming of protoplasm occurs) and the structure holding the valve together. These glamour shots of the diatom revealed a unique bridge design that encased the raphe, maybe this was part of the answer they were trying to uncover. Alas, after taking these first few photographs they never made it to the apical part of the diatom to see the most complex part of the structure. Shortly thereafter in 1979, at age 83, Conger was hit by a bicyclist and did not recover from the injuries, still with plans to write a paper on the subject of B. paradoxa.
Conger’s lifelong devotion to microscopy is one to honor; he transformed what had been seen as a chore into a delicate artform. Reluctant to retire at the mandatory age of 70 (and hoping an exception would be made for him) he continued to come to work. He could finesse the invisible into revealing all its secrets, and his steady unbothered work created a foundation for many to come after him. Unfortunately his position was voided after he passed, and his office remains quiet. To Robinson, “the Scanning Electron Microscopes (SEM) have revitalized two fields of botany: palinology and diatomology,” and subsequent work studying B. paradoxa and its mode of protoplasm streaming continues. For Conger, though, the pleasure was in the process. In being patient. The work of discovery is eternal as the nature of life is to change. A continuous cycle of exchange witnessed by those who take the time to watch stillness.
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