Page:Popular Science Monthly Volume 83.djvu/237

Rh tissues; and even seedlings often displace comparatively large masses of soil in pushing up through.

For several years we have been observing the rupturing of very hard concrete by ostrich ferns (Onoclea Struthiopteris L.). The concrete, which is two and a half to three inches thick and composed of sand, tar and coarse gravel, acts as a watershed next a dwelling house. Along the edge ostrich ferns were some time ago planted in loam rich in organic matter, and have since been growing most luxuriantly, the stalks often reaching a height of six feet or more. Like most ferns, the underground stem or rhizome spreads out in all directions each year and thrusts up new fronds; and quite regardless of the apparently impenetrable covering, the rhizomes work their way under it and attempt to throw up new shoots. And not in vain, for the ferns appear to break through the concrete as easily as though it were so much putty. This rupturing occurs almost every spring when growth is active and the fronds unfolding. Sometimes the concrete is broken up where it joins the underpinning of the house and where it is more easily dislocated, and again the ferns come up through the middle.

The fronds which push themselves up through the concrete are necessarily more backward in unfolding than the unobstructed ones, although as a rule it requires only a week or ten days for them to break through. It required two years for one group of fronds to come through, though, as was evident from the constant upheaval of a part of the concrete one spring; but the next spring they succeeded in their attempt. The ease with which this breaking through is accomplished and the freedom of the ferns from scars and injuries are remarkable