TWO TYPES OF VARIABLE PUBESCENCE ON PLANTS 
P. L. RiCKER 
Pubescence on plants has long been made use of by systematic 
botanists as a character upon which species are frequently based, 
wholly or in part. In instances in which this combined with other 
constant characters it may be of value, but observations in the field 
and herbarium covering a long period of years have led to the belief 
that in a much larger proportion of cases than is suspected pubescence 
has been a delusion and a snare to the systematist. To most system- 
atists doubtless a hair is a hair unless these differ noticeably in struc- 
ture, size, or abundance, and little or no thought is given to the 
function of hairs or their possible lack of diagnostic value. 
It is probable that all pubescence on plants, and perhaps glauces- 
cence, may be divided into two classes, viz.: functioning and non- 
functioning. As an example of the latter class may be cited the well- 
known and extremely variable Paspalum floridanum Michx., in almost 
any patch of which one may find at least six forms as follows: 
1. Plants with only the basal leaves and sheaths pubescent. 
2. Plants with the basal leaves and sheaths and the sheaths of all 
cauline leaves pubescent. 
3. Plants with all leaves and sheaths pubescent. 
4. Plants with all leaves and sheaths and the stem pubescent as far 
as the rachis. 
5. Plants pubescent to the tip of the inflorescence. 
6. The more glabrous forms are in some cases glaucous. 
In this species at least, the pubescence may be the result of a muta- 
tion and does not vary throughout the season. At least it does not 
appear to have any definite function. What would be the results of 
a study of the progeny of each form is uncertain, but probably the 
majority of the offspring would be like the parent with a scattering 
of all of the other forms. 
In plants with functioning pubescence are found greater possi- 
bilities of deception to the systematic botanist than in the former. 
It has long been observed that the leaves of certain plants lose their 
470 
