246 



KNOWLEDGE 



[No\-EMBER 1, 1898. 



Fig. 1. — Rotifer iuliabiting the hood 

 of a Scale-Moss. (After Keruer.) 



plants which have no true power of digestion are yet bene- 

 fitted by capturing insects ; from the decomposing bodies 

 of their victims products are evolved which the plants are 

 able to assimilate. 



The water-vessels of the Bromelias and allied epiphytes, 

 which often contain half a pint or more of water, are 

 particularly interesting. The hollow leaf-base in some 

 of this group of plants is a veritable aquarium. The water 

 which accumulates in these curious receptacles Fritz 

 Miiller found to be inhabited by caddis-fiies, entomo- 

 stracans, and aquatic 

 beetles belonging to 

 species not occurring 

 elsewhere. A small frog 

 even takes up its abode 

 among the bromelian 

 leaves. Species of Utri- 

 cularia also occur — small 

 aquatic plants which cap- 

 ture in their curious little 

 bladders the tiny crusta- 

 ceans inhabiting the 

 water in the bromelia 

 leaves where they grow ! 

 r. nelumhifolia in this 

 way grows in the leaves 

 of Tillandsias, which are 

 themselves epiphytes on the branches of other plants. 



The term symbiosis is applied to those curious relation- 

 ships in which we find two organisms of different kinds 

 living together in partnership for mutual benefit and 

 protection. A remarkable example of such symbiotic 

 association is afforded by certain rotifers which take up 

 their abode in the pitcher-like leaflets of some Junger- 

 mannias. One of these liverworts {Fndlania dilattita) 

 growing on the bark of species of Acer has hollow 

 appendages of this description in which the water is 

 retained by capillary attraction. In each of these pitchers 

 a rotifer (Callidina symbiotu-a) takes up its quarters, finding 

 in this retreat food and shelter. The association in all 

 probability is one of mutual advantage ; the rotifer is 

 supposed to make a return to the plant for its entertain- 

 ment in the shape of excrementitious products. 



The case of these liverworts and rotifers is particularly 

 interesting in connection with some recent observations 

 made by the writer. In making sections of the chickweed 

 stem to examine the origin of the lateral rootlets referred 

 to in the preceding article, it was noticed that there 

 frequently appeared on the slide specimens of the slipper- 

 animalcule, ParamcBcium, for whose presence it was 

 difficult to account. So frequently did this infusorian 

 put in an appearance that at last the idea suggested itself 

 of its being a regular inhabitant of the water that gathers 

 in the leaf axils of the chickweed. The examination of a 

 number of specimens left little doubt as to the fact of this 

 organism as well as several others frequenting the leaf 

 axils of the plant in question. On submitting water from 

 the leaves of a number of other plants it became apparent 

 that leaf axils are rather favourite resorts for the minuter 

 forms of life. Rotifers or wheel-animalcules, infusorians, 

 monads, desmids, diatoms, micrococci and bacteria are of 

 common occurrence. Paramfficium appeared to be rather 

 characteristic of the chickweed, but was also present in the 

 leaves of the sow thistle. In the leaves of the latter we 

 also found that beautiful, lUy-like infusorian the bell- 

 animalcule, Vorticella cyathnia. Rotifer vulgaris occurs 

 more or less frequently in the axils of the self-heal and 

 ox-eye daisy. In none of the leaves examined could ento- 

 mostracans be detected, although Cypris and other 



copeopods abounded in pools close to where the plants 

 grew. The absence of the latter may be due to their size, 

 entomostracans being very much larger than rotifers. 



Although most of these organisms are to be found in all 

 sorts of places where rain-water collects, their abundance 

 in the tiny droplets that lurk in the leaf-axils of the plants 

 just mentioned affords an interesting illustration of how 

 Nature crowds her canvas, striving to utilize every nook 

 and cranny that offers to living things the least coign of 

 vantage. 



Infusorians and rotifers, as is well-known, may be dried 

 and reduced to powder without losing their vitaUty. After 

 they have lain dormant for months the addition of a little 

 water at once recalls them to life and activity. It is, 

 therefore, in the highest degree probable that in their 

 desiccated state they get blown along with dust into the 

 axils of the leaves, and are revived by the water that 

 trickles down into their resting places after a shower. 

 Still, in the case of the rotifers, at least, there is another 

 possibility. The wheel-animalcules are exceedingly active 

 little creatures. Their mode of progression somewhat 

 resembles that of the worms, with which they have close 

 affinities. Mr. A. R. Wallace mentions in his "Travels 

 on the Amazon " the remarkable fact that in some parts 

 of Brazil, during the wet season, when the lands where 

 they live are flooded, the large earthworms ascend trees 

 and take up their abode in the hollow leaves of a species of 

 Tillandsia, where they are often found accumulated by 

 thousands. There is therefore nothing at all improbable 

 in the idea that a rotifer may reach its station in the axil 

 of a leaf, like these South American worms, by climbing. 



Although only bearing remotely on the present subject, 

 we may recall the case of Rosa Banksia?, Acacia spadicigera, 

 and other myrmecophilous plants where the hollow leaf- 

 bases form the headquarters of the garrisons of ants by 

 which these plants are defended. 



The facts now referred to go to support the view of 

 Kerner, that in those plants where aerial absorption occurs 

 the object may 

 be not so much 

 sec u r i t y 

 against 

 drought as to 

 obtain a sup- 

 ply of nitro- 

 genous mate- 

 rials. Both 

 ends are pro- 

 bably attained, 

 for leaves, as 

 we have seen, 

 are capable of 

 assimilating 

 compounds 

 of nitrogen. 

 But whether 

 the absorption 

 take place at 



the roots or at the leaves it is evident that contrivances 

 for promoting self- irrigation are all the more important 

 on account of the nutritive salts which rain-water may 

 hold in solution. 



The prevalence of micro-organisms in leaf-axils suggests 

 a probable origin of the carnivorous character ; and though 

 it may be difficult or impossible to estabhsh a truly 

 symbiotic relationship between any of them and the 

 plants on which they live, these observations, nevertheless, 

 touch the threshold of a large, inviting subject, practically 

 unexplored. 



f lo. 2. — Animals inhabiting the axils of leaves. 



1 and 2, Rotifer vulgaris ; 3 and 4, Tortieella ; 



5, Paramcecium ; 6, Entomostracan. 



