A SUMMARY OF THE REVISED EDITION. 



The Key to the various Families based 

 K e ' ' upon leaf form and flower character should 



be useful to those who prefer to hunt down 

 a strange specimen by this means. But it is necessary 

 to give close heed to the many exceptions to rigid rule. 

 These exceptions are recorded as faithfully as possible 

 throughout the Key. Often a plant is opposite-leaved 

 at the base and alternate-leaved at the top Lythrum 

 alatum, for instance in such a case the form of the older, 

 lower leaves is alone recorded with other important 

 characters of the plant. 



Not infrequently it is the case that the leaves are so 

 crowded on the plant-stem one cannot tell whether they 

 are alternate or opposite. But the Key always records 

 the fact, and it is the alternating leaf which usually does 

 the crowding. In the use of the term "circling" I do 

 not mean that kind of a leaf which is apparently pierced 

 by the plant-stem, but the one which with its fellows 

 encircles the stem ; the technical term for such an 

 arrangement is whorled. Whorled leaves are, of course, 

 opposite. 



In the last part of the Key certain leaves like those of 

 the Cat-tail are called " blade-shaped," perhaps a more 

 acceptable term would have been sword-shaped ; but I 

 use the word blade in the same sense as one uses it in 

 connection with grass. Needless to say a small pocket 

 magnifying glass is essential to every one who desires 

 seriously to study flowers. The counting of stamens or 

 an examination of the character of style and pistil, or 

 even the smooth or hairy surface of a leaf or a plant- 

 stem should not be attempted without the assistance of 

 a lens. The Key's usefulness is really dependent upon 

 the study of plants with optical aid, such a method of 

 procedure is consequently the only way to use a very 

 small Key with which to open a very large door 

 successfully. 



F. SCHUYLER MATHEWS. 

 CAMBRIDGE, March, 1912. 



