218 THE MICROSCOPE. 
Wolle has identified the following species: Denticula valida, 
Denticula elegans, Navicula major, Navicula viridis, Epithemia 
argus, Epithemia argus var., Amphicephala, Epithemia hyndmannii, 
Cocconema cymbiforma, Achnanthes gibberula, Mastigloia smithii, 
Fragillaria. The first named species was the most abundant, 
forming the bulk of the specimen. The white pulverulent material 
at the margin of the bog proved to consist of the dried remains of 
these same diatoms, and it is quite evident that this diatom ooze is 
forming a bed of diatomaceous earth. Subsequent investigation 
shows that a diatom ooze, consisting of the same species forms the 
chief constituent of similar marshes all over the park. It has also 
been found that the meadows of the geyser and hot-spring basins 
were once marshes of this character, and are underlaid by beds of 
soft straw-colored or gray material which consists of the partially 
dried remains of diatoms. This material when dried is white, 
loosely coherent, soils the fingers, and consists either entirely or very 
largely, of diatom tests. These diatom beds cover many square 
miles in the vicinity of active or extinct hot-spring vents of the 
park, and are often three feet, four feet, and sometimes five to six 
feet thick. 
MEAsvREMENT OF Poxien.*—Prof. Byron D. Halsted, has meas- 
ured forty-one kinds of pollen taken from twenty orders of plants, 
and finds that not only is there a considerable difference in range of 
sizeof the grains, but that in measuring, the condition of the pollen, 
that is, whether it is dry or wet, must also be considered. Pollen 
when dry, that is, freshly taken from the dehisced anther, shows 
some things not seen in the same when wet. Of course, the natural 
shape of the pollen is destroyed by the wetting process. Many 
grains have characteristic folds which are lost from view when 
liquid expands the coats. Only one of these folds is usually seen 
in side view, but by looking at one end there are usually three ob- 
served. Some grains, like many kinds of mint pollen, are flat; that 
is,somewhat flax-seed shaped. In monarda fistulosa, for example, the 
grains are 34 x.$4u when viewed flatwise, and each grain is trav- 
ersed by three folds, making the grain resemble a miniature musk- 
mellon. When water is added the grain changes its shape with 
surprising rapidity, the longer diameter becomes the shorter and the 
shorter the longer, with little variation in the original figures. Dry 
pollen has the outer coat uniform, while in the wet grains there 
may be broad belts or lines of a different exterior. The pores are 
not usually so evident in the dry pollen as when they are wet. It is 
* Bull. Torrey Botan. Club, May, 1889, page 135. 
