260 TEXTBOOK OF BOTANY 



temperature of the winter months. These conditions disappear much 

 more slowly in some species than in others. As soon as they have 

 disappeared, both flower and leaf buds of many woody plants will grow 

 if the plant or stem cuttings are placed in a warm room and supplied 

 with water. Often root fonnation occurs at the base of the cuttings. If 

 the conditions causing dormancy have not disappeared, the plant may 

 slowly die. 



In recent years the vapor of certain chemical compounds" has been 

 used to shorten the period of dormancy in the buds of many plants. The 

 dormant period of buds of Irish potato has been experimentally shortened 

 from one to four months, depending upon the variety tested. In the lati- 

 tude of New York some of the common shrubs, such as lilac, flowering 

 plums, crabs, and quinces, if exposed to vapor of ethylene chlorhydrin 

 in December will bloom within a month. The plants or twigs should 

 be placed within a tight box containing 1 ounce of ethylene chlorhydrin 

 for each 8 cubic feet of space. After two days they should be trans- 

 ferred to a warm room or greenhouse. If these artificial treatments are 

 applied early in autumn the results are unsuccessful. Treatment with 

 temperatures near freezing for three or four weeks in early autumn 

 before ethylene chlorhydrin is applied shortens the dormant period still 

 more. Methods for breaking dormancy in buds are at present in an 

 experimental stage of development but anyone may try them on some 

 particular plant. Storage at low and high temperatures, drying, wound- 

 ing, and treatment with special chemicals have all been used to 

 shorten the dormant period of buds. Diverse results have been obtained 

 with different plants. 



This chapter contains a brief account of external similarities in stems 

 and of some of the usual differences in form and habit of growth that 

 may be found. Ordinarily stems may be recognized by the presence of 

 one or more characteristic external features, such as nodes, leaves, and 

 leaf scars. They may be herbaceous or woody, aerial or underground. 

 They may vary in form from the cylindrical stems of trees, shrubs, herbs, 

 and vines to tendrils, thorns, and the short thick stems characteristic of 

 succulents, tubers, corms, and bulbs. Most stems bear leaves, flowers, 

 and branches. Under certain conditions roots may also grow as lateral 

 organs on many kinds of stems. The fonii of the plant and its type of 

 branching are dependent on the relative development of branches from 



^ Ethylene chlorhydrin, ethylene dichloride, edier, carbon bisulfide and many others. 



