2 THE PLANT WORLD 



supply for the next summer. Most of these second-growth fronds are 

 small and sterile, while true fertile ones are rarely ever formed. Instead 

 we find a whole series of forms. Some are merely sterile ones with the 

 pinnae deeply cut into obtuse lobes ; hence the name obtusilobata 

 which was given this form. Some of the.se fronds become more deeply 

 lobed with their margins more or less revolute, thus approaching the 

 fertile type, as is shown also by the presence of scattered indusia that 

 look like whitish .scales on the under side (5). Some of these pinnae 

 have the lower lobes contracted while the upper ones are flat and spread- 

 ing; or only the lower pinnae may be contracted while the tip of the 

 frond is nearly normal. These fronds are shorter-stalked than the ones 

 less deeply lobed. From them it is but a .step to still shorter fronds 

 with smaller and more revolute lobes that begin to bear sporangia as well 

 as indusia. The limit with these mutilated plants seems to be reached 

 when fronds are produced with the divisions berry-like, but smaller than 

 usual, and with the pinnae spreading instead of growing nearly parallel 

 with the stalk. This one little point shows that they have not entirely 

 lost their sterile character, if we may so express it. Still other fronds 

 are completely sterile on one side, but bear normal fertile pinnae on the 

 other. 



The ostrich fern {Stndhiopteris Germanica) has fertile pinnae that 

 are commonly described as being "pod-like or necklace-shaped." The 

 two halves of each pinna are rolled in toward the midrib, thus forming 

 two tubes enclosing the sporangia. A cross-section of a pinna reminds 

 one of the muzzle of a double-barrelled shotgun, but the surface of the 

 pinna shows constrictions here and there corresponding to the spaces 

 between the lobes of the pinna. Hence the use of the word " necklace," 

 for the pinna may suggest a double row of beads. When the ostrich fern 

 is cut down early in the summer it may also send up what we will call 

 ' 'obtusilobata ' ' forms for lack of any other name. We are less familiar with 

 this species than with the sensitive fern, for it is not only rare but it also 

 fruits very sparingly in Maryland. The illustration (8) was made from 

 a specimen sent from A. A. Eaton of New Hampshire, who wrote that 

 the "ferns were cut down ju.st before fruiting (July 2) and these came 

 up." The upper part of the frond and the tips of the middle pinnae are 

 like those of small sterile fronds except that the lobes are represented by 

 large teeth and the edges show a tendencj- to be revolute. The latter 

 becomes more pronounced at the bases of the middle pinnae. To gen- 

 eralize, passing from the tip to the base of the frond, or of a middle 

 pinna, it is first wholly leaf-like, then .scattered indusia appear and the 

 edges become more and more revolute. In my .specimens there appear to 

 be no spore-cases, and the lowest pinnae do not look quite like the true 

 fertile ones. 



