THE PO]yER OF GROWTH IN PLANTS 



233 



W' 



catc 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 con- 

 crete, 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 ap- 

 parently 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. 



Fig. 3. Showing epi- 

 cotyl of seedling burst- 

 ing through the soil. 



Fig. 4. Showing young fronds of ostrich ferns (Onoclea Struthiopteris L.) 

 rupturing concrete. 



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 



