VI 



Introduction 



The key to the families, as well as those to the genera and species, is as simple as the 

 necessary drill in flower structures and relationships will permit. The keys are based on the 

 method of alternatives, e. g., I. Petals present; II. Petals absent. The two alternatives, rarely 

 more, are indicated by being indented equally, and by the same series of signs, e. g., 1 and 2, 

 a and b, (x) and (y), etc. At every step the beginner must consider both alternatives before 



III. Leaf Edges 



making a choice, in order to make sure 

 of tracing a plant readily and certainly. 

 Terms should be looked up in tin- glos- 

 as they appear, and their meaning 

 fixed in mind. The temptation to guess 

 at the points of structure necessary for 

 following the key must be constantly 

 avoided in order to obtain trustworthy 

 results. When unusual flower types ap- 

 pear in a family, the family may occur 

 more than once in the key, or the genus 

 concerned may be given, as "Prunus in 

 Rosaceae." 



FLOWER TYrES 



The flower type, which is regarded ;.s 

 the simplest or earliest form from which 

 the types of the various families have developed, has the four parts: calyx, made up of 

 sepals, corolla, made up of petals, stamens, and pistils. The normal or usual flower has 



12 3 



1. Serrate (saw-toothed). 



3. Crenate (scalloped). 

 5. Sinuate (bayed). 



4 5 6 



?. Dentate (toothed). 

 I. Undulate (wavy). 



6. Incised (jagged). 



IV. Leaf Tips 



Acuminate. 

 6. Emarginate 



V. Lobed Leaves 



2. Acute. 3. Obtuse. 4. Truncate. 5. Retuse. 



7. Obcordate. 8. Cuspidate. 9. Mucronate. 



sepals, petals, stamens 

 and pistils. Flowers oft- 

 en occur in which one or 

 more of these parts is 

 lacking. Petals are most 

 frequently absent, while 

 sepals are often lacking 

 also. Sepals are some- 

 times colored like the 

 petals, as in lilies, and seem to be lacking when they are not. When only one kind of flower 

 leaves is present, it is regarded as the calyx, regardless of its color. Stamens may disappear 

 in one flower, and pistils in another, giving rise to staminate and pistillate flowers, as in 



many of the trees. Both 

 rarely disappear from the 

 same flower in nature, 

 though this frequently 

 happens in cultivation, 

 especially in "double" 

 flowers. 



The simplest flower 

 type, seen in the flower 

 of the buttercup, or the 

 mousetail, is made up of 

 separate sepals, petals. 

 stamens, and pistils. All 

 the sepals are alike, as 

 are the petals, and the 

 number of stamens and 

 pistils is large. The four 

 parts are practically at 

 the same level, the sepals 

 outermost and the pistils 

 innermost. The changes 

 from this simplest type 



Divided. 

 Divided. 



