USE OF KEYS 1 5 



completed, we are obliged to resort to a more or less artificial 

 grouping of many plants, purely as a matter of convenience. 



The Use of Keys. — In using keys as an aid in the determin- 

 ation of plants, there are certain precautions which should be 

 observed. Perhaps the most important of these is that the key 

 will unlock nothing unless the characters of the plant in hand 

 are first understood. A preliminary examination of the flower 

 and its parts is especially desirable, and care should be taken in 

 gathering material to see that all stages from the young plant 

 to the mature fruit are represented as far as possible. If the 

 beginner will select plants with large flowers for his first trials, 

 and especially if he will take the trouble to write out their 

 characters, with the aid of our introductory lessons and glossary, 

 he will avoid much of that confusion which results from an im- 

 perfect understanding of plant descriptions. Due allowance must 

 always be made for a certain amount of variation in plants, 

 especially as to size. When a number of specimens of one species 

 are available, it is well to select an average one for study rather 

 than either of the extremes, for descriptions are seldom drawn in 

 such a way as to include the unusual or abnormal forms of a 

 species. 



The first step in determining the name of a plant is to decide 

 upon the family to which it belongs. In our Analytical Key to 

 the Families the first division separates off the Fern Group, which 

 is the only family of the so-called flowerless plants here described. 

 Division II (Flowering Plants) includes all plants which bear 

 true seeds. Formerly they were called Phaenogamia and were 

 characterized as producing true flowers. Of this great division 

 there are two sub-divisions, as will be seen by reference to the 

 key, (1) the Gymnosperms, which are represented with us only 

 by our cone-bearing trees and the so-called California Nutmeg, 

 and (2) the Angiosperms, which latter class includes the bulk 

 of our species. The beginning student of the Yosemite Flora will 

 probably be but little interested in that part of our key preceding 

 the line, "Subdivision 2, Angiosperms." 



The next segregation, into the class of Monocotyledons and 

 the class of Dicotyledons, is based upon so many characters that 

 the student seldom goes astray here. The fact that so many sets 

 of characters run parallel in the two groups of families strength- 

 ens our belief that this segregation is a natural one. In fact, 

 all of the divisions so far have been based on natural relation- 

 ships. Leaving, now, the first class, let us take up the second, 

 which is by far the larger and therefore the more difficult. We 

 here find the Dicotyledons segregated into an apetalous, a chori- 

 petalous, and a sympetalous section, a classification which is 



