142 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
doubt to Amerpohli, have also had their position changed, and on the basis 
of close resemblance have been placed with the sports of Whitmani to which 
they are probably related.^ 
The Nature of Regressive Variation 
It is common knowledge that some of the Boston-fern varieties as they 
are obtained from the florist fail to remain entirely true to type. The 
most familiar manifestation of this aberration occurs in some of the division 
forms: thus, in a plant of some twice or thrice pinnate variety there may 
appear one or more once pinnate leaves, and similar leaves may continue to 
be developed together with the typical leaves of the given variety. The 
resultant plant often shows a distressingly mixed or mongrel appearance. 
This sort of reversion is, however, only one of several types, the others 
being relatively frequent in florists' estabHshments. The purpose of the 
present paper is to describe these various types of reversion, both the prod- 
ucts and, as far as possible, the processes. The term ''reversion," which 
will be used interchangeably with ''regressive variation," is here applied 
to any modified form which shows a change from some progressive variety 
back toward hostoniensis. Thus, the production by a vaiiety with leaves 
twice or more pinnate of leaves less divided than the typical form is called a 
reversion. The production by a dwarf form of a plant with larger leaves 
is also considered as reversion, and likewise the reduction of ruffling. 
Broadly, we may recognize three manifestations of such reversion. 
1. The simplest possible type is seen in the appearance of single aberrant, 
i.e., reverting leaves among others which are typical. This is a common 
occurrence in varieties in the division series. 
2. Again, we may find all the new leaves of a single crown or stem axis 
appearing reverted in form; e.g., in a plant of a thrice-divided variety the 
typical leaves may be succeeded by once pinnate leaves developed one at a 
time until the former appearance of the crown is entirely altered. 
3. The third type of reversion occurs when the change in character 
takes place in one of the branch reproductive shoots or stolons, and appears 
only when from this stolon new bud plants develop which manifest the new 
character (PI. IX, fig. i). 
The first two types may be designated as "crown" reversion, partial 
and complete, and the second may be called "runner" reversion. Only 
the crown type may be actually watched in the external manifestations of 
the process. Runner reversion is know^n only in its products, i.e., the new 
forms developed as bud plants on lateral stolons. The cytological changes 
^ It may be of interest to some to know that a considerable set of varieties of these 
Nephrohpis sports may be obtained from John Lewis Childs, Floral Park, New York. At 
present the Childs catalogue lists 30 different forms representing all types of variation 
listed in the chart, both progressive and regressive. The stock plants are grown sepa- 
rately, and the identification of the varieties offered may be generally relied upon. 
