302 



Canadian Record of Science. 



or is it simply a case of distribution in space ? An examination 

 of the a normal pinna shows that its length bears the relation to 

 the length of the modified pinna, of 1:1.75. In the normal 

 pinnae the veinlets number 8 per centimetre, and they there- 

 fore have an average interval of 1.25 mm. In the modified 

 pinnae, on the other hand, the midribs of the pinnules which 

 are, of course, the anatomical equivalents of the veinlets in the 

 normal pinnae, number 1.66 per centimetre, and they are there- 

 fore seperated by an average interval of 6.03 mm. We discover 

 from this that in undergoing alteration, the veinlets of the nor- 

 mal pinnae have become separated in the pinnules in the ratio 

 of 1:4.80. Such a relation at first suggests a simple extension 

 of parts, but while the veinlets become separated by an inter- 

 val nearly five times greater than normal, the corresponding 

 alteration in longitudinal dimensions of the pinna, in its trans- 

 formation into the compound form, shows an increase of only 

 three-fourths of the original dimensions. It is therefore ob- 

 vious that the change has involved an actual obliteration of 

 parts to the extent of one-fourth of the vascular structure as 

 represented in the original veinlets. 



Fig. 10. Nephrolepis exaltata 

 piebsoni. Base of compound pinna 

 showing at a the somewhat enlarged 

 auricle ; at b the first pinnule, and be- 

 tween on both sides, the potential pin- 

 nules as exhibited in the lobes, x \ 



Fig. 11. Nephrolepis exaltata 

 piersoni. Base of a compound pinna 

 showing at a the first pinnule with a 

 corresponding development at a' 

 bb the first pinnules and b' the first 

 free pinnule, x \ 



We now come to the relation which these changes in ex- 

 ternal form bear to the reproductive process. This plant is 

 said to become modified only with respect to its sterile fronds, 

 which is substantially the same as saying that the variety cannot 

 be reproduced through spores since we must recognize that 



