354 THE AMERICAN NATURALIST. [Vol. XXXVIII. 



interest. Reference to the table of anatomical data will show 

 that the change from bordered to simple pits is entirely confined 

 to the genus Pinus, and that it does not rise abruptly as if in 

 response to some unusual condition whereby a profound altera- 

 tion in the usual course of development was induced ; but it is 

 effected by stages, showing that whatever influences were 

 brought to bear, they operated gradually through a somewhat 

 prolonged period of development, while here and there strong 

 tendencies to reversion were manifested, and that the alteration 

 was finally effected in a permanent way, only in the most highly 

 developed pines. Commencing with P. lambertiana it will be 

 observed that some species of the soft pines are characterized by 

 simple pits. Among the hard pines P. clmisa and P. rigida 

 have bordered pits, while the six following species again show 

 simple pits. We next come to a group of four species, with one 

 exception (P. murrayand) Japanese, in which there is a mingling 

 of both bordered and simple pits, showing a decided persistency 

 of the primitive character in the face of conditions which involve 

 a change. Following these are two species with simple pits, one 

 with transitional features, five with simple pits, one with bor- 

 dered pits, one with the transitional form and the remaining six 

 species with simple pits, only. It will therefore be seen that 

 these changes occur in waves, and that within the limits of forty- 

 one species there are three complete and six incomplete recurrent 

 phases. If we were arguing from purely theoretical grounds, all 

 of these species should be arranged in such order as to show, 

 (i) bordered pits, (2) transitional forms and (3) wholly simple 

 pits, and we should thereby gain a perfect, developmental 

 sequence. But such a position would not be justified by other 

 evidence of an equally, if not more weighty character, and it is 

 our object to interpret the facts as they are found. It has 

 already been shown that the occurrence of simple pits in the 

 pines is consonant with a higher type of development, and that 

 the change is not only accompanied by sporadic reversions or 

 survivals as one may choose to regard them, but that the change 

 as a whole is a process of reduction. From this point of view 

 then, we must regard the occurrence of bordered pits in P. 

 clausa, P. rigida and P. pungeiis as pure survivals of a more 



