in Thoreau’s Journal:
Having noticed the pine pollen washed up on the shore of three or four ponds in the woods lately and at Ripple Lake, a dozen rods from the nearest pine, also having seen the pollen carried off visibly half a dozen rods from a pitch pine which I had jarred, and rising all the while when there was very little wind, it suggested to me that the air must be full of this fine dust at this season, that it must be carried to great distances, when dry, and falling at night perhaps, or with a change in the atmosphere, its presence might be detected remote from pines by examining the edges of pretty large bodies of water, where it would be collected to one side by the wind and waves from a large area.
So I thought over all the small ponds in the township in order to select one or more most remote from the woods or pines, whose shores I might examine and so test my theory. I could think of none more favorable than this little pond only four rods in diameter, a watering-place in John Brown’s pasture, which has but few pads in it. It is a small round pond at the bottom of a hollow in the midst of a perfectly bare, dry pasture. The nearest wood of any kind is just thirty-nine rods distant northward, and across a road from the edge of the pond. Any other wood in other directions is five or six times as far. I knew it was a bad time to try my experiment, —just after such heavy rains and when the pines are effete, —a little too late. The wind was now blowing quite strong from the northeast, whereas all the pollen that I had seen hitherto had been collected on the northeast sides of ponds by a southwest wind. I approached the pond from the northeast and, looking over it and carefully along the shore there, could detect no pollen. I then proceeded to walk round it, but still could detect none. I then said to myself, If there was any here before the rain and northeast wind, it must have been on the northeast side and then have been washed over and now up high quite at or on the shore. I looked there carefully, stooping down, and was gratified to find, after all, a distinct yellow line of pollen dust about half an inch in width —or washing off to two or three times that width —quite on the edge, and some dead twigs which I took up from the wet shore were completely coated with it, as with sulphur. This yellow line reached half a rod along the southwest side, and I then detected a little of the dust slightly graying the surface for two or three feet out there. (Many little snow (?) -fleas on it.)
When I thought I had failed, I was much pleased to detect, after all, this distinct yellow line, revealing unmistakably the presence of pines in the neighborhood and thus confirming my theory. As chemists detect the presence of ozone in the atmosphere by exposing to it a delicately prepared paper, so the lakes detect for us thus the presence of the pine pollen in the atmosphere. They are our pollinometers. How much of this invisible dust must be floating in the atmosphere, and be inhaled and drunk by us at this season! Who knows but the pollen of some plants may be unwholesome to inhale, and produce the diseases of the season?
Of course a large pond will collect the most, and you will find most at the bottom of long deep bays into which the wind blows.
I do not believe that there is any part of this town on which the pollen of the pine may not fall. The time to examine the ponds this year was, I should say, from the 15th to the 20th of this month. Looking at the trees today, I find that the pines are now effete, especially the pitch pine, the sterile flowers now turned reddish. The white pine is lighter-colored, and all but a very little indeed is effete. In the white pine it is a dense cluster of twenty or thirty little flowers about the base of this year’s shoot.
I did not expect to find any pollen, the pond was so small and distant from any wood, but I thought that I would examine. Who knows but the pollen of various kinds floating through the air at this season may be the source of some of the peculiar perfumes which are not traceable to their sources?