58 



KNOWLEDGE, 



[March 1, 1899. 



doubt due to the width of the dispersal of the spores that 

 they find these situations, which are, one would suppose, 

 comparatively few. It is probably from this delicacy of 

 the requisite conditions for success that plasmodia are not 

 unfrequently seen to fail in the struggle of life. They will 

 sometimes reach the surface, and commence the formation 

 of the sporangium walls and spores, and then fog off and 

 decay, without ever reaching maturity or producing sound 

 spores. 



The observations with regard to the influence of heat, 

 drought, light, and darkness, on plasmodia may be correct, 

 but it does not follow from them that the needs of the 

 organism dependent on the stage it has reached, or on 

 other circumstances unknown to us, may not also operate 

 on their motions. We know that the sporangia are pro- 

 duced on the surface, but we hardly know whether the 

 organism seeks the surface when it is time to develop 

 sporangia, or develops sporangia when it reaches the 

 surface. 



Negative Geotbopism.— It is not only in the motion of 

 the Plasmodium as a whole, but in the motion of its parts 

 when it develops sporangia, that we observe an upward 

 movement. Sometimes, no doubt, the sporangia are 

 developed on the under surface or the side of the wood on 

 which they grow. We are inchned to think that different 

 species prefer different situations for the production of 

 their sporangia, and that no one law is applicable to them 

 all ; but in all cases the sporangia appear to stand vertically 

 to the plane on which they grow. 



If we examine the trunk of an oak, we find an elaborate 

 structure of hard parts which maintains the tree in its 

 upward growth, and by the force of cohesion resists and 

 overcomes the force of gravity drawing it downwards. 

 If we examine the stalk of even a delicate flowering 

 plant, we find that it is constituted of cells, and that the 

 cell walls, as well as the fibres, afford to the stem a 

 certain amount of support ; but in the naked protoplasm of 

 the myxie we have no woody tissue, no cell wall, and yet 

 this, too, lifts itself away from the earth and towards the 

 Bun and the air. We then see that the upward motion of 

 plants does not depend on cell walls, but is an inherent, an 

 original capacity of some protoplasm. 



We can easily appreciate the advantage which this 

 upward tendency gains for the organism, for it lifts it into 

 the air and exposes it to the influence of light. We know 

 the great results on the surface of the earth of this so- 

 called negative geotropism. If all plants had crawled 

 along the ground hke the thallus of Marchantia or the 

 hyphoe of some fungi, we should have had a keener com- 

 petition for surface space even than now exists, and we 

 should have lost the beauty with which the earth's surface 

 is clothed. In the myxie lifting up its sporangia, we can 

 see in the small and in its simplest and most primitive 

 form, the existence of the same power which enables the 

 sequoia or the eucalyptus to lift themselves to such enormous 

 heights above the ground. But of this power, this im- 

 pulse, this faculty, this gift of resisting the force of gravity, 

 and the attraction of the earth— what shall we say ? what 

 account can we give ? We can only keep silence. 



Captueing Food.— The habits of swarm spores in the 

 pursuit or capture of their food have been very successfully 

 observed by Mr. Lister. In the case of Pcrichmia cortiralis 

 he observed a swarm spore with four vacuoles, each stuffed 

 with from six to eight bacilli ; and in the course of twelve 

 minutes he saw four bacilli drawn in by the projecting 

 parts, or pseudo-podia of the swarm spore. In the case 

 of Didymium (or Cliondnoderma] di forme, he observed 

 that the capture of a bacillus is sometimes effected by 

 pseudopodia. More often, a funnel-shaped aperture was 



formed in the posterior part of the swarm spore, and when 

 a bacillus was unwary enough to enter, it was enclosed by 

 a folding over of the lips of the funnel. The bacilli thus 

 captured were seen to dissolve in the vacuoles, but no 

 refuse matter was observed to be rejected ; probably the 

 whole bacillus was of absolutely digestible matter. On 

 another occasion, Mr. Lister observed a swarm spore come 

 upon a group of motionless bacilli. It spread itself out 

 so as to cover four of them, and in about two minutes 

 resumed its former shape, and crept away, carrying two 

 bacilli in its vacuole. In the case of Stemoiiitis fusca,,he 

 observed the capture by pseudopodia of a bacUlus so large 

 that when drawn up into the body of the swarm spore it 

 forced the swarm spore to bulge out on either side. On this 

 followed a violent jerking motion of the swarm spore, which 

 frequently occurs after the ingestion of food, and in a few 

 minutes the bacillus was bent double, and the vacuole 

 decreased in size. These observations of Mr. Lister seem 

 to prove that the view of De Bary that the swarm spores 

 take in nutriment only in a fluid state cannot be upheld. 

 These processes are depicted in Fig. 3, which is repro- 

 duced by the permission of the Council of the Linnean 

 Society and of Mr. Lister. 



It is a curious fact that where a Plasmodium on its 

 march meets with a microcyst of its own kind, it has 

 been observed to commit an act of cannibalism — to treat 

 it as if a foreign body, and to enclose it in a vacuole, 

 and then absorb it. Probably the presence of the mem- 

 brane prevented fusion until it was removed by an act of 

 digestion. 



Rejection of Matter. — Mr. Lister has been equally 

 successful in observing the method pursued by the Plas- 

 modium in the rejection of undigested matter. He fed, 

 and I am afraid overfed, the plasmodia of Badhamia 

 titricularis on thin slices of fungus, and when a Plasmodium 

 had become loaded with food material, many of the large 

 vacuoles became charged with undigested matter, which 

 assumed the appearance of a dark ball, and he " repeatedly 

 saw these vacuoles push out as bubbles to the surface of 

 the Plasmodium and burst, discharging a cloud of refuse, 

 consisting of fragments of starch and broken fungus 

 hyphce, into the water." But when the plasmodium creeps 

 over glass, he observed the rejected matter, with a certain 

 amount of plasmodium substance, to be left " on each side 

 of the retreating veins, leaving a mass of the network after 

 the Plasmodium has withdrawn." 



In other cases rejected matter, particles of starch or 

 spores of algfe, or other things which have been taken up 

 by the plasmodium, are found thrown aside in the hollow 

 cavity of the foot of the sporangium, or even amongst the 

 contents of the sporangium itself. 



Notices of JJoofes. 



> 



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