410 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
exhibits a great period, dependent on internal causes. There is a con- 
nection between the apical and the secondary growth, the two curves 
coinciding ; the maximum of apical activity corresponds to the greater 
length of the zone of growth ; both processes are influenced by external 
agencies. Similar laws apply to the growing point of the root. In 
the case of annual woody plants, growth in thickness (growth of the 
secondary meristem) exhibits a periodicity dependent on internal causes, 
corresponding to the periodicity of the primary meristem, but indepen- 
dent of it. The formation of an annual ring is the immediate con- 
sequence of spontaneous and periodic changes in the activity of the 
cambium ; the periodicity in the activity of the cambium is indepen- 
dent of that of the primary meristem, although both are influenced 
by external conditions. 
Rhythmic Growth in Plants.* — Mr. T. Meehan adduces a number 
of examples of the effect of “rhythmic growth ” in producing apparent 
irregularities in the growth of plants. To this he attributes the occasional 
irregularity and the dimorphism in the flowers of Phlox and other genera 
of Polemoniaceae. The so-called “ polarity ” of the leaves of Silphium 
laciniatum and other “compass-plants” is due to the same law. In 
many cases (e.g. Gleditschia ) , glands are the result of the arrested de- 
velopment of a branch — another illustration of the action of this law. 
The author points out also the small amount of evidence of the occur- 
rence of hybrids in nature, even when the conditions appear to be specially 
favourable to the crossing of different species. The forms often regarded 
as hybrids he believes to be varieties dependent on the operation of the 
law of rhythmic growth. 
Growth of Allium ursinum.j — Herr A. Rimpach notes a periodicity 
in the development of this plant. In the autumn, slender roots which 
are not contractile spring from the primary axis ; also slender lateral 
roots from those formed in the previous spring. At the same time the 
bulb, consisting of a bud and a single leaf, begins to grow ; the foliage- 
leaves developing in the course of the winter. In the spring the leaves 
appear above ground, and quickly unfold, the old bulb-leaf disappearing. 
Contractile roots are now formed, which drag the plant downwards into 
the soil. The foliage-leaves, the innermost of which is transformed into 
a receptacle for food-material, continue their function till August, when 
they wither. 
Growth of Colchicum autumnale.J — In this plant Herr A. Rimpach 
finds that the gradual sinking of the corm in the soil is not effected by the 
agency of contractile roots, or not to any appreciable extent. This de- 
pression takes place year after year, until the corm has sunk to a depth of 
about 15 cm., which may require about 20 years. After that it remains 
nearly stationary. Growth begins in the late summer or autumn, by the 
production of numerous slender roots at the time when the flowers 
expand. The assimilating period of the leaves lasts from April till July. 
Fleshy roots make their appearance in April or May, which have a strong 
resemblance to the contractile roots of other underground stems, but 
. * Proc. Acad. Nat. Sci. Philadelphia, 1897, pp. 178-81, 191-3, 194-6, 196-9. 
t Ber. Deutsch. Bot. Gesell., xv. (1897) pp. 248-52 (1 pi.). 
j Tom. cit., pp. 298-302 (1 pi.). _ 
