638 EXPERIMENT STATION RECORD. [Vol. 38 



whether the quantitative relations between the starch content and sugar content 

 remain constant throughout the latter part of the growing season and to throw 

 some light on the determination of the best time of harvesting the crop. 

 Samples of from 15 to 20 kg. of roots were collected each week from September 

 18 to November 27, inclusive, and moisture, starch, cane sugar, and reducing 

 sugar determined in duplicate in 5 potatoes of each lot. The results of the 

 analyses are presented in tabular form, illustrated graphically, and briefly dis- 

 cussed. The author also compares his observations with those made by Keitt 

 in South Carolina (B. S. R., 25, p. 534). 



It is concluded " that the changes occurring in sweet potatoes in the ground 

 during the latter part of the growing season proceed in a regular and orderly 

 manner. During the later part of the period of growth the composition of 

 the roots remains remarkably uniform, and presents no striking or irregular 

 fluctuations. During this period the root is characterized by a high starch 

 content and a low sugar content. The changes which occur later are associated 

 with the death of the vines. Prominent among these changes is the accumula- 

 tion of water in the roots as a result of the cessation of transpiration in conse- 

 quence of the destruction of the leaves. With the termination of the flow of 

 materials from the vines the carbohydrate transformations characteristic of 

 sweet potatoes in storage are inaugurated. These changes consist in the trans- 

 formation of starch into sugars. In point of time the decrease in starch and 

 the increase in reducing sugar precede somewhat the increase in cane sugar. It 

 appears, therefore, that reducing sugar is formed first as an intermediate 

 step in the change from starch to cane sugar. The loss caused by respira- 

 tion, which is considerable during the curing process and in storage, is ap- 

 parently slight in sweet potatoes in the ground. Appreciable destruction of 

 carbohydrates appears not to occur under these conditions until late In the 

 season when the roots have been injured by frosts. 



" The changes here described have a practical bearing on the question of 

 maturation of sweet potatoes and on the choice of the time of harvest. . . . 

 It is evident . . . that the choice of time of harvest is not a matter of maturity 

 of the roots, but is governed by other factors. The potatoes may safely be kept 

 in the ground until the leaves have been injured by frost. Of the changes 

 which occur after the destruction of the leaves, the accumulation of water 

 in the roots deserves foremost consideration. It can scarcely be doubted that 

 this increased water content is detrimental to the successful storage of the 

 roots, and causes them to be more subject to decay than roots of normal water 

 content. . . . On this account it is of utmost importance that the harvesting 

 of sweet potatoes be not long delayed after the leaves have been killed by frost. 

 The other changes occurring in sweet potatoes in the ground are essentially 

 the same as the changes occurring in storage. These changes are therefore in 

 no way detrimental to the crop, since no appreciable loss of carbohydrates 

 occurs until the roots have been so severely injured that they have lost their 

 market value." 



Tobacco culture in Eg-ypt, V. Moss6bi {Bui. Union Agr. Egypte, 15 (1917), 

 No. 119, pp. SS-7S, figs. 2). — A detailed account of tobacco production under 

 Egyptian conditions. 



Structure of the pod and the seed of the Georgia velvet bean, Stizolobium 

 deeringianum, C. V. Piper and J. M. Shxji.l (U. S. Dept. Agr., Jo-ur. Agr. 

 Research, 11 {1917), No. IS, pp. 673-676, pis. 2).— The microscopic structure 

 of the pod and seed of S. decringianum is described and illustrated. Since 

 velvet bean meal gives promise of becoming an important commercial feed 

 these structures are deemed important as a basis of identifying the meal either 

 pure, adulterated, or in mixtures. 



