172 BIOLOGICAL LECTURES. 



stood to be the fertile leaf in the experiment plat, and the 

 knife was used for the third time. While cutting the third 

 crop of leaves occasionally one was seen which appeared quite 

 different from the ordinary sterile leaves. The pinnules were 

 fully expanded, and the lobes appeared nearly normal in form, 

 but the venation was somewhat more prominent, and this gave 

 the appearance which first attracted attention. After critical 

 examination there were seen peculiar and very small whitish 

 flakes or scales on the under surface of the pinnules. These, 

 with the aid of a pocket lens, were readily seen to be partially 

 aborted indusia, located either directly across or at the side of 

 the veinlets. The pleasure at the discovery of this result was 

 considerably dampened by the thought that the experiment 

 might prove to have been too radical by cutting the leaves 

 more than once. Further examination revealed what appeared 

 to be still younger fertile leaves which would not be so fully 

 expanded when grown. At this date there were observed in 

 the adjacent undisturbed plants several normal sporophylls 

 partially developed. July 29 another examination was made, 

 and quite a number of leaves were found which would be taken 

 for quite typical cases of the form of the species. 



August 8 and 9, all the plants showing these results were 

 gathered and photographed, a portion of the stem, or rhizome, 

 was taken with each plant in order to show some, at least, of 

 the bases of the leaves which had been amputated, as well as 

 the recently developed sterile leaves for comparison. Nearly 

 thirty such plants were gathered, and more than twenty of these 

 were photographed, in order to preserve an accurate record of 

 the many variations which presented themselves. 



In the normal sporophyll, the pinnae are quite closely 

 approximated on one side of the rachis. The fertile pinnules 

 are closely revolute, and the margins very much shortened, so 

 that each pinnule forms a small, oval, pocket-shaped or slipper- 

 shaped sack, open only at a point near the attachment with 

 the mid-vein of the pinna. These pinnules possess two to four 

 pairs of lateral veinlets. Upon these lateral veinlets are the 

 placentae, seated rather near the base, and the true indusium 

 is situated across the base of the veinlet, near, or a little dis- 



