CHAPTER IX.—MODE OF LIFE OF THE MYCETOZOA. 449 
The requisites for germination are the same in sclerotia and cysts as in 
spores, as was stated above on page 428, where also will be found all that is known 
of the external causes which lead to the formation of these states. 
Section CXXVII. Some account has necessarily been already given in section 
CXIX of the phenomena attending the life of the plasmodia. For many 
general questions which here come under consideration, the reader is referred, in ac- 
cordance with the purpose of this book, to works on general physiology, and especially 
to Pfeffer’s Physiology, vol. II, chap. 8 and Stahl’s latest publication on the subject, 
and the account here given must be confined to a short review of their mode of life. 
This has been investigated chiefly in the plasmodia of the Physareae, Fuligo especially, 
which are readily procured. What is known of other forms appears to agree 
with the accounts given of the.Physareae, but. requires. more exact investigation. 
Movement of plasmodia. The internal causes of the changes of shape, of 
the protrusion ‘and withdrawal of processes and the interior streaming of granules, 
which are attendant on the organisation of the protoplasmic body and are 
to a great extent unknown to us, cannot of course be discussed in this place. 
The most important external causes of the movements of the plasmodium and 
of the changes in its form are, the z//umination, the distribution and movement of the 
water in the substratum, the chemzcal nature of the environment, and the conditions of 
temperature. It is uncertain to what extent purely mechanical influences are also 
operative. Rosanoff’s former assumption of ,geotropic movements has proved to be 
without foundation. We may therefore, in accordance'more or less with the general 
terminology of the movements of growth, speak: of phenomena of Aeliotropism, 
Aydrotropism and rheotropism, trophotropism and thermotropism. 
Heliotropism. A vegetating plasmodium stretches out its branches and 
reticulations uniformly in every direction on uniformly moistened surfaces, such as 
paper steeped in water and kept in a dark or equably but faintly illuminated chamber. 
If. the intensity of the illumination is increased, the power of movement, according to 
Baranetzki, is generally diminished, and if the amount of illumination is different in 
different portions of the expanded surface, the branches are drawn in from the bright 
side and others are put forth towards the darker side; the plasmodium also moves 
towards the darker side. The direction of these movements is independent of the 
direction of the beams of light which fall-on the plasmodium, being determined only 
by the intensity of the illumination. 
Hydrotropism. : If while all other conditions are uniformly favourable the 
water is unequally distributed in the substratum, the vegetating plasmodia, if not on 
the point of forming spores, withdraw from the drier spots when the dryness has 
reached a certain degree and wander towards the moister. 
Rheotropism. If a stream of water is made to flow slowly through a 
moistened porous substratum, such as filtering paper or strips of linen cloth, the 
plasmodia which are vegetating on the moist surface wander in the direction cf 
the stream, without regard to the particular direction in space in which it moves. 
Trophotropism. Vegetating plasmodia spread out on surfaces which yield 
little or no nutriment move towards bodies which contain nutrient substances as 
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