15° The Botanical Gazette. [May, 



that the application of the Baranetzky auxanometer to a study of their 

 growth is either unknown or rarely practiced. No record of such use 

 can be found. The writer therefore ventures to note a method of set- 

 ting up the apparatus, for this purpose, which is now being employed 

 with good results in the botanical laboratories of the University of 

 Minnesota. 



Potatoes are selected that make the tubers habitually some distance 

 from the base of the aerial stem. The soil is removed through a 

 separable side of the culture-box and a tuber is exposed. This is 

 blocked up rigidly from below . in such a manner that no downward 

 movement of the tuber can take place. A jacket made of two small 

 square pieces of cigar-box wood is now fitted on the upper and under 

 sides of the tuber, the lower piece resting on the block below. The 

 pieces are held around the tuber by means of very slender rubber- 

 bands and by small cleats on their faces which grip the tuber gently. 

 The upper of these squares of wood is furnished with a central screw 

 to which the thread of the tracing wheel is attached. The whole is 

 then covered with soil and the side of the box replaced. The smoked 

 cylinder is now brought into position, the battery and clock connected 

 and the tracing-needle adjusted. The clock should be set to release 

 the armature every three hours. Now, when growth takes place in 

 the tuber, since no movement downward can ensue, the thread is re- 

 leased and the tracing-needle makes a vertical stroke, indicating the 

 growth. (See Vines : Physiology p. 399; Sachs : Physiol. Eng. trans. 

 p. 557; Pfeffer : Pflanzenphysiologie II, p. 86; Detmer : Handbuch 

 Pflanzenphys. p. 257; Goodale : Physiol. Bot. p. 383.) 



Experiments made up to date indicate but do not demonstrate a 

 daily periodicity in the growth of the potato tuber. If such is the case 

 two explanation* would at once suggest themselves. Since the 

 apparent maximum of growth in this organ lies between 10 P. m. and 8 

 a. m. it might be compared with aerial shoots and the rhythm be con- 

 sidered a hereditary trait, as the embryonic positive-hebotropic 

 curvature of ivy shoots. More reasonable, however, would be the 

 other explanation, co-ordinating the daily rhythm of the tuber with 

 the rhythmic production of starch in the assimilating surfaces. 



A more extended series of experiments along this line is being con- 

 ducted by Mr. C. P. Lommen and he will doubtless be able to speak 

 more fully upon the matter later on. This note merely calls attention 



to the method of -tudy. 



nesota. 



>f 



A monstroH form of a common lieW daisy.— The plant which I am 



about to describe was received from Virginia where it was found 



