BOTANY: A. M. HURD 
201 
SOME ORIENTING EFFECTS OF MONOCHROMATIC LIGHTS OF 
EQUAL INTENSITIES ON FUCUS SPORES AND RHIZOIDS 
By Annie May Hurd 
Botany Department, University of California 
Communicated by J. M. Coulter, April 11, 1919 
One of the most striking of the biological phenomena resulting from the 
action of light on organisms is the orientation of the first cleavage plane of 
germinating spores by unilateral illumination. Whenever such illumination is 
sufficiently intense the first cross wall forms perpendicular to the direction of 
the incident light. This phenomenon has been demonstrated in Equisetum, 
Puccinia, Fucus and some other algae^'^-^'^^-^^ together with the fact that the 
cell on the shaded side of the spore becomes the rhizoidal cell irrespective of 
gravity. Thus in these and related forms the polarity of the plant is estab- 
lished by the direction of light stimuli. 
The power of light waves to so orient the plant is, without doubt, the 
power to orient the spindle of the first dividing nucleus. The mechanics of 
such reactions may long remain unknown; but we have a suggestive and pos- 
sibly the ultimate explanation in Child's^ metabolic gradient theory. He has 
demonstrated in many marine plants and in some of the lower animals the 
existence of the so-called 'axial gradients.' By an axial gradient is meant 
the decreasing rate of metabolic processes from the apical to the basal end. 
We may suppose that such a gradient is produced within a germinating spore 
whenever there is sufficient difference in the amount of light energy received 
on two opposite sides to produce the requisite difference in the rate of the 
oxidation processes along the line of direction of illumination. If Child's 
supposition is correct, the cell on the shaded side of the spore becomes the 
rhizoidal cell by virtue of the fact that the least rapid rate of the oxidation 
reactions along the gradient determines the basal end, the most rapid the 
apical end, of the organism. 
The purpose of the present investigation was to study the power of pure 
monochromatic lights to establish the polarity of the germinating spores of 
Fucus inflatus, and also to answer several questions concerning the negative 
phototropism of the young rhizoids; viz., the determination of the exact wave 
lengths responsible for the phenomenon; the relative importance of the quality 
and quantity factors in the illumination or the role of intensity of illumination 
apart from the kind of light; and whether all effective monochromatic Hghts 
produce the same result as white light. 
To obtain the monochromatic light, seven Wratten filter screens were used, 
each transmitting a narrow range of wave lengths but altogether embracing 
the whole of the visible spectrum. The wave lengths to which each screen 
was transparent were determined by testing the light transmitted by each with 
