﻿BOTANICAL GAZETTE 



Physiological 



Immature potatoes have a thin, slightly suberized skin, which 

 is quite permeable to both water and gases. As the tubers mature, 

 the skin becomes more suberized and more adherent to the under- 

 lying tissue. The rapidity and degree of suberization, however, is 

 greatly influenced by moisture; dry conditions favor the process, 

 while moisture retards it. As the skin becomes suberized, its 

 permeability to water and gases is greatly reduced. It occurred 

 to the writer that the skin may very soon become a sufficient 

 barrier between the internal tissues and the external agents to 

 check growth in the buds. This might be due to an external agent 

 becoming a limiting factor in the completion of the growth mechan- 

 ism in the new tuber, or in the growth itself. The following experi- 

 ments were planned to test this hypothesis: 



The fall crop of McCormick potatoes furnished material for the 

 experiments here recorded, except where otherwise noted. All the 

 experiments, however, were repeatedly confirmed with the summer 

 crop of both Green Mountain and Rehobeth potatoes. The regular 

 mature crop of the McCormick potatoes was harvested on Novem- 

 ber 4. Tubers were at once planted in the greenhouse in soil, saw- 

 dust and sphagnum, but in no case did sprouting occur until 

 January 18 ; general sprouting did not begin until February. These 

 results were confirmed by similar plantings of McCormick potatoes 

 in 3 successive years. The rest period of McCormick potatoes 

 under natural planting conditions, therefore, is about 90 days from 

 the time the mature crop is harvested at this station. If they are 

 harvested earlier, the rest period is much longer. Immature tubers 

 harvested on September 20, and immediately planted in the green- 

 house, did not sprout until February 2. 



Effect of removing the skin.— Simply removing the skin from 

 potato tubers at any stage of the rest period will bring about sprout- 

 ing within 10 days, if favorable external conditions prevail. A num- 

 ber of methods were employed in order to supply the most favorable 

 conditions for sprouting; but the best among those tried consisted 

 in planting the stem ends in wet soil or sawdust and covering the 

 seed ends with 2 or 3 inches of excelsior, kept constantly wet. This 

 method exposes the terminal buds to the maximum partial oxygen 



