1887. | BOTANICAL GAZETTE. 281 
investigation into the action of light, moisture and gravitation upon the 
production of tubers, especially those of the potato; or, as the author has 
concisely stated it in the first sentence of the introductory chapter, “ The 
subject treated in the following pages is the problem, what causes deter- 
mine the position and growth of tubers.” The potato was used for most 
of the experiments, being especially well adapted for the purpose. Be- 
sides the potato, Helianthus tuberosus and Ullucus tuberosa, the latter a 
South American esculent, were studied as examples of annual tubers, and 
two species of Begonia for perennial tubers. The author refers to de 
Vries’ memoir (Landw. Jahrbiicher for 1878) for a critical review of most 
of the literature pertaining to the subject. 
The variety of potato chiefly used for the experiments is one not 
commonly grown in this country; it is known in Germany as the “six- 
weeks potato,” in France as “ marjolin,” and its peculiarity consists in 
usually producing a thick leafless growth at one end during the period of 
rest, being the expansion of the terminal bud. 
By many ingenious experiments it was established that light exerted 
a retarding influence upon the growth of the tuber, and that a certain 
range of temperature was also desirable. Tubers may occasionally be 
produced above ground in the light, as is known not only from casual ob- 
servation but as proven by earlier investigators. The author showed from 
is own experiments that the potato stem is verticibasal; that at its base 
it normally produces, besides the roots, the tubers, and at the apex the 
foliage. When a plant is grown from a reversed cutting, the tubers are 
produced upon the proper base of the stem, which is now above ground 
and in the light. Tubers can also be produced above ground by using a 
cutting which has only part of one internode sunken in the soil, so that 
no node is below the ground to give off subterranean stolons. Another 
method is to start the tuber, and when the roots around the base of the 
shoot are of some length, to remove the old tuber and leave the stem en- 
tirely above ground but with the roots in the soil. The base of the stem, 
which is now above ground, produces tubers. Tubers formed above 
ground are small, but it was found that if the light was excluded from 
such a tuber it grew to the usual size. 
pace does not permit a further mention of experiments or even & 
ull statement of the results. It must suffice to say that the author con- 
cludes that the position and the growth of the tuber and the deposition 
of starch in the same are separable processes; that gravitation has very 
little or nothing to do with determining the position of tubers, but that 
it depends for the most part upon internal causes ; and that light has a 
strong retarding power on their development. 
The work is an excellent example of physiol 
ogical research carried 
on with inexpensive apparatus and without the employment 
scope. 
of a micro- 
