168 
long, upper 1% inches; rhachis straight; spikelets pale, in 
four rows, crowded, elliptical-oblong, acute, nearly 1% lines 
long; sterile glumes sparingly pubescent, three to five-nerved. 
This is described from a single specimen collected by Dr. Buck- 
ley in Texas. It is nearest to P. Avidum, from which it differs 
in its longer panicle, with more numerous, longer and more distant 
spikes, and in the form and pubescence of the spikelets, 
The Dehiscence of Fern Sporangia. 
An easy and convenient method of studying the interesting 
process of the bursting of the sporangium in ferns is the fol- 
lowing: 
Place some sporangia from a. mature sorus of any of the 
Polypodiacez (an herbanium specimen will do) in a drop of water 
on a slide and cover with a thin cover glass. The dehiscent 
sporangia will soon close; now examine their structure, espec- 
ially the cells forming the annulus. Notice that their outer peri- 
pheral walls are much thinner than the inner and radial ones. 
Apply a drop of glycerine, chloriodide of zinc or sulphuric acid to 
one edge of the cover glass, and draw off the water by a piece of 
blotting paper at the opposite edge. While the water is slowly dis- 
placed by the reagent, concentrate the attention on the cells of the: 
annulus; observe that the, radial walls gradually approach each 
other, while the outer curve inward and finally double up. This 
decreases the size of the cells, and-hence the length of the outer 
curve of the annulus; the latter gradually becomes straight, and 
finally recurved, so that the ends often touch one another. The 
tension exerted on the thin-walled portion of the sporangium by 
the straightening of the annulus has,:meanwhile, caused it to 
burst. Suddenly, however, the cells of the annulus resume their 
former shape, it at once becomes straight, and the. sporangium 
slowly assumes the shape which it had before it was placed in 
the water. If the cells of the annulus be now examined, it will 
be noticed that each contains an air-bubble almost entirely filling 
its cavity. If the reagent be replaced by water the bubbles will 
become globular, grow smaller and smaller and finally disappear-. 
At the same time the annulus cells expand to their full size, the 
sporangium closes entirely and is now in the condition in which it 
