234 INFLUENCE OF CORRELATION AND EXTERNAL STIMULI 



Sachs l has shown that the branching of the protonema of mosses, 

 especially in the case of Funaria hygrometrica, is influenced in a similar 

 manner by light. ' Light acts upon this plant in such a way that the 

 vegetative points of the lateral shoots arise only on the flanks of the 

 mother-shoot when these are illuminated chiefly from one side.' I must 

 however point out that protonemata grown in darkness, and which on 

 account of their nourishment in sugar-solutions had reached a relatively 

 great size, exhibited a two-rowed position of the branches upon the chief 

 axis (Fig. 114), and therefore in this case there exists the tendency to 

 distichous branching, and it is only the plane of this which is determined 

 by the light. That the construction of the protonema is dependent upon 

 outer factors, the case of Ephemeropsis, which I have described, shows '*. 



The protonema of this plant is epiphytic on 

 leaves ; it bears twigs upon its back and upon 

 its flanks, and from the former arise the flat 

 broad lateral twigs which serve as organs of 

 assimilation :! . 



In concluding this subject a few other 

 relationships of configuration of Bryophyta upon 

 which light has a directive influence may be 

 cited : 



In the Bryophyta we frequently observe a 

 displacement of the leaves from their original 

 transverse insertion upon the shoot-axis in the 

 bud to an oblique position, or, as in the extreme 

 case of Schistostega, until the line of insertion 

 coincides with the long axis of the stem itself. 

 From my investigations I conclude that in many 

 cases light has a direct influence upon this. 



Plants of Jungermannia bicuspidata and of 

 Plagiochila asplenioides (Fig. 115) placed in 

 light of very low intensity developed positively heliotropic shoots 

 in which frequently 4 the transverse position of the leaves was retained, 

 the displacement being suppressed. In another Jungermannia with 

 leaves having a more elongated insertion, there was displacement even 

 in etiolated shoots. Schistostega occupies a somewhat peculiar position 

 amongst the mosses, because its leaves are arranged in two longitudinal 

 series on the vegetative stem (Fig. 25). In the bud an original many-rowed 



FlG. 115. Plagiochila asplenioides. 

 Stem seen from above. The dorsal 

 edge of each leaf is inserted lower 

 down on the stem than the ventral 

 ed(;e. ,S sporogonium. Natural size. 

 Lehrb. 



1 Sachs, tiber orthotrope und plagiotrope Pflanzenteile, in Aib. d. bot. Inslituts in \Yiirzburg, ii. 

 p. 256; Id., Lectures on Physiology of Plants, p. 527. 

 - Goebel, in Ann. du Jardin botanique de Buitenzorg, vii. 

 :< For more details on this point see Part II of this book. 

 4 In Plagiochila particularly the phenomenon was partial. 



