SCIENCE-GOSSIP. 



secrete a honey-like fluid greatly enjoyed by them, 

 and solid food is also provided in the shape of 

 small "fruit-like bodies" found on the leaflets 

 when they first unfold ; these ripen at intervals and 

 are then most acceptable to the ants, which con- 

 tinually run about the young leaves seeking for 

 fruits in a suitable condition, and thus prevent 

 injury, at the most critical time, from the depreda- 

 tions of other creatures. This species of ant seems 

 adapted for this particular tree and is not found 

 anywhere else. Moreover, when Mr. Belt sowed 

 some of the acacia seeds in his own garden in 

 another part of the country, where the Pseudomyrma 

 did not exist, the seedlings at once fell a prey to 

 the leaf-cutter ants, while in their native district 

 they were protected by their own insect 

 companions. There seems reason to believe the 

 spines are not fully developed in cases in which 

 the ants do not tenant them, so that an actual 

 modification of the plant in the insects' favour is 

 brought about in the majority of instances. Such 

 a close relationship and mutual dependence as is 

 here implied, of obvious benefit to both parties, is 

 very remarkable, especially when existing between 

 a plant and an animal so self-reliant and free as an 

 ant. It almost amounts indeed to symbiosis, and 

 may well be taken as leading us to a consideration 

 of that condition. 



Symbiosis means " having the same life," and in 

 the connections described by the term, the organ- 

 isms usually are actually connected by more or less 

 complete bodily union, sometimes even to the 

 extent of appearing as one to a careful observer. 

 The examples of this condition are most of them of 

 interest to microscopists, and it is in that connection 

 especially I should like to treat them, particularly 

 as many may be studied without trouble or 

 difficulty by the " home naturalist." The various 

 small marine animals now knov/n as Radiolarians 

 (formerly Polycystina), and some of the Foramini- 

 fera also, have embedded in the jelly-like substance 

 of their bodies certain yellowish cells or granules ; 

 these, after having all sorts of theoretical functions 

 assigned to them, are now almost universally 

 believed to consist of true algae, living symbiotically 

 in the " sarcode " of the animal. They, in most 

 cases, have a cellulose wall, nucleus, with colouring 

 matter at least resembling the chlorophyll of the 

 higher green plants, and appear like them to be 

 able to excrete oxygen and form starch under the 

 influence of light. It is conceivable that they use 

 the carbon of their hosts as the basis for the starch 

 production, as well as that contained in the water. 

 It is quite probable that the oxygen they give off 

 and some surplus portion of the starch are avail- 

 able for the use of their living homes in return for 

 the protective shelter afforded them. 



It is not necessary to go so far for examples of 

 what at least may be similar cases. Every 



microscopist is acquainted with specimens of pond 

 life of a colour identical with the algae that are their 

 neighbours. Hydra viridis referred to in Science- 

 Gossip (Vol. ii., N.S., p. 276), various species of 

 Stentor, Coleps, Paramecium, and others, are of this 

 tint. It has been asserted that owing to the 

 presence of symbiotic algae in their body-walls, and 

 in consequence of the presence of the plants, the 

 animals are able to flourish with a greatly reduced 

 food-supply, or even to bear its entire cessation for 

 a time that would be fatal but for the assistance 

 afforded by their indwelling companions, who 

 procure it as already described in the case of 

 the Radiolarians. It is true this theory is by no 

 means so freely accepted as in the previous instance. 

 If, as some of those even who oppose it in its 

 entirety admit, the green colour is due to the 

 presence of chlorophyll corpuscles, though not of 

 actual algae, it certainly looks like the correct 

 explanation, for chlorophyll is undoubtedly the 

 most typical and characteristic distinction between 

 plants and animals, physiologically considered. 



Strasburger, in his " Handbook of Practical 

 Botany," gives an interesting instance which has 

 the advantage of being easily observed by most 

 microscopists. There is a small floating plant 

 called Azolla; it is one of the Rhizocarps, a group 

 of the vascular Cryptogams, and is closely allied to 

 the ferns. It looks like a small fern frond and is 

 from half to three-quarters of an inch in length. 

 It consists of a stem with bright green pinnate 

 leaves on each side, which float on the surface 

 of water, having underneath membranous lobes 

 immersed. The upper lobes are swollen or inflated, 

 and have a cavity or hollow inside which communi- 

 cates with the water through an opening on the 

 inner side of the leaf, and growing from the walls 

 into the cavity are long hairs, in some species at 

 any rate. In the cavities in the leaflets of the 

 living Azolla dwells another plant, one of the lower 

 Algae, named A nabcena ; it belongs to the Nostocaceae 

 and consists of rows of small bead-like cells, bluish 

 green ; at intervals a larger cell slightly differing in 

 colour occurs, which is called a heterocyst ; I 

 believe the purpose of these is not known, but 

 probably they have some connection with re- 

 production. The leaflets containing the Anabcena 

 may be pulled to pieces with needles on a slip in a 

 drop of water, then on putting on a cover glass and 

 pressing slightly, the little algae can easily be seen. 

 A half-inch objective with B eyepiece, say about 

 no to 130 diameters, is sufficient, though a 

 considerably higher power is better. Horizontal 

 sections may be cut by laying the Azolla on a piece 

 of cork or even on the finger, and making cuts from 

 base to apex with a razor. Some are almost sure 

 to show the chambers opened by the razor, and the 

 Anabana inside. The slices mount nicely in 

 glycerine or glycerine jelly, if the usual precautions 



