PLASMODIA: CIRCVLATTON OF PROTOPLASM. 615 



Plasmodia again disappear from the surface, creeping into the interior of the tan, 

 to come forth once more on the renewal of darkness : this may be repeated 

 several times during the course of the day. According to the statements of 

 Baranetzky', it appears also that plasmodia which have crept up glass plates, and 

 there become extended in the form of elegant networks, withdraw themselves from 

 those places which are intentionally illuminated, and become collected at the 

 shaded ones. This irritability to light, however, only exists during a certain 

 condition of life of the plasmodia; when their internal development is so far 

 completed that they are proceeding to the formation of sporangia, &c., they make 

 their appearance on the surface of the tan even when the light is strong. I have 

 also already noticed the remarkable creeping of the plasmodia up the stems of 

 plants, up flower-pots, and other objects, sometimes very high. They may 

 be impelled to do this very easily, by placing moistened glass plates vertically 

 in the tan, which contains young plasmodia just about to creep on to the sur- 

 face ; in the course of a few hours the reticulated masses ascend the glass plates up 

 to the highest points, and they may now be removed and placed directly under 

 the microscope, in order to observe their internal movements more in detail. There 

 is probably little doubt that this impulse to creep upwards is to be regarded as 

 a geotropic stimulation — i.e. that a still unknown action of gravitation on the 

 molecular structure of the protoplasm so affects the displacements of the molecules 

 that the result mentioned follows. It is, however, scarcely necessary to say that 

 the individual mechanical processes in the matter are entirely unknown. 



In all essential points the so-called Circulation of the protoplasm ^ in the interior 

 of living cells agrees with the movement of plasmodia ; only in this case the 

 extent of the space within which the motions of the protoplasmic body can occur 

 is once for all determined by the resistant cell-wall. It has already been described 

 and illustrated by figures on pp., 80-82 how this comes about, when the cells 

 at first entirely filled with protoplasm grow by absorbing water, whereby in the 

 first place small water cavities or vacuoles appear in the interior, and how the 

 water or cell-sap then increases more and more, so that in the subsequently much 

 enlarged cell the protoplasm constitutes a more or less thick sac, everywhere 

 closely applied to the inside of the cell-wall and enveloping the cell-sap, traversing 

 which are strand-like or plate-like filaments of protoplasm, and how all is in move- 

 ment. The accompanying figure, reproduced from my Handbook, will contribute 

 still more to give the reader an idea of the protoplasm thus in circulation. The 

 latter is represented in the figure as a finely pimctated mass in which lie larger 

 bodies also, especially chlorophyll granules which contain starch; in one place 

 also is to be seen a small crystal of calcium oxalate. It is practically the move- 

 ments of these small granules or microsomes and the larger bodies which betray 

 the streaming movement of all parts of the protoplasm; only an outermost layer, 



' Baranetzky, 'Influence de la lumiere sur les Plasmodia det Myxomycetes,' Mem. de la soc. 

 nat. des scienc. nat. de Cherbourg (T. XIX. 1876). 



" Dr. Klebs has carefully collected the literature on circulation and rotation as well as on all 

 the movements of the protoplasm here referred to in the 'Biologisch. Centralblatt^ ed. by Rosenthal, 

 1881 (Nos. i6, 17, and 19). 



