1386 THE NATURE-STUDY OF PLANTS 
Occasionally the Herb Robert has pure white 
flowers, and there are two charming and well-marked 
forms, rather than varieties in the same sense as the 
shingle variety: the leaves and stems may show 
either the red- or the brown-green with which we are 
familiar, or else be of a beautiful bright green without 
any suggestion of either of the other colours ; neither 
form is by any means common, and both of them are 
worthy not only of notice but also of study. 
It will again add very greatly to the value and 
interest of the student’s work if he will take the 
opportunity, whenever it offers, of comparing the 
particular species that he is observing with its near 
relatives. In England we have a dozen species of 
Geranium or Cranesbill and three of Erodium or 
Heronsbill, to say nothing of their varieties and 
forms, so that anything like a comprehensive com- 
parative study of their natural history would be a 
very large order indeed. With the exception of the 
Dusky,* the Wood7 and the Round-leaved Cranesbill,t 
most of the Geraniums occur pretty commonly, if 
not always wild, whatever the correct interpretation 
of that somewhat difficult word may be, whereas two 
of the three Erodiums are rare or local. I propose 
offering a few hints as to how to set about a business 
of this sort, illustrated by some of my own observations. 
Until the reader has had a good deal of experience 
as a Nature-student he will be wise to ignore the first 
two factors of life, for observations and experiments, 
comparative or otherwise, about respiration and 
nutrition cannot be made in the field, but only in the 
laboratory. 
* Geranium pheum, Linn. + Geranium sylvaticum, Linn. 
t Geranium rotundifoliwm, Linn. 
