io8 Science of Plant Life 



may be seen in the tulip tree and the magnolias of temperate 

 climates. The buds of most temperate perennials are covered 

 with scales. Not infrequently the scales are further covered 

 with matted hairs and secretions of wax and resin. These all 

 tend to make the bud coverings impervious to water. In this 

 way the tender growing parts are protected from excessive loss 

 of water during the winter and during the still more critical 

 stage in early spring when the buds are opening. 



We are likely to think of buds as being formed at about the 

 time when the leaves fall from the trees. A good observer, 

 however, will have noted that the buds begin to develop when 

 the leaves unfold in spring, and that they grow all summer 

 long. Because of the prominence of the leaves, the buds are 

 obscured somewhat during the summer months, and become 

 conspicuous only after the leaves are gone. 



The opening of buds. When the warm weather of spring- 

 time comes, the innermost bud scales begin to grow and 

 expand. Sometimes the outer scales are pushed off; some- 

 times they elongate and grow like the inner ones. But the 

 scales quickly reach their full growth, and soon they are cut 

 off by the formation of an abscission layer at the base of each. 

 In the buds of a few plants all the scales are dead and are 

 pushed off by the growth of the stem and leaves inside. The 

 expansion of bud scales and leaves takes place almost wholly 

 through the enlargement of cells already formed. Within 

 the bud the minute leaf cells absorb water and develop large 

 vacuoles. The expansion of these cells results in the en- 

 largement and spreading of the leaves. Material for the study 

 of the different habits of bud expansion may be secured in 

 winter by bringing branches of different kinds of trees into a 

 warm room and placing them in water until the leaves expand. 



