NOVKJIBER 1, 1900.] 



KNOWLEDGE. 



245 



invests the root of its hasfc without poiietr.'vting it-s cclln 

 is of simihu- service is not certain. 



The myoorhiza is found especially upon roots which 

 grow in soils rich in decaying humus. It is also in- 

 variably present in the roots of plant*; growing in sucii 

 soil which possess little or no chlorophyll in their stems 

 and leaves, such. e.fl.. as the ground oixhids. It is there- 

 fore probahlc that it is in some way serviceable in 

 supplying its host with such organic substances as arc 

 formed during the decay of plant (/(7>r('<.f These 

 may be merely conveyed by the fungus in an unaltered 

 condition into the tissues of its host; on the other 

 hand it may be that they undcrgft within the cells of 

 the fungus such changes as render them more easily 

 absorbed and assimilated by the green plant. It has 

 also been suggested that another, perhaps the chief, 

 duty of the fungus element of the mycorhizal partner- 

 ship is, in some cases, connected with the supply of 

 suitable compounds of Nitrogen to the more prominent 

 partner. Fungi absorb certain compound.^ of ammonia 

 — such as are found in the soil — and, by the activity of 

 their protoplasm, build thenr up into more conijjlcx 

 organic compounds. It is at lea.st possible that this may 

 be the nature of the contribution whicli the fungus 

 makes to the plant in or upon whose roots it lives. But 

 to what extent any or all of these relationships exist 

 between the flowering plant and its mycorhiza can only 

 be detennined by future reseai'ch. At present we must 

 conclude that the tmc significance of this form of asso- 

 ciation between green plants and the more lowly organ- 

 ised fungi requires further elucidation ; there is, 

 however, no doubt that it is of considerable importance 

 in the economy of nature. 



We have now considered the pnncipal sources of the 

 food-supply of green plants and the channels by which 

 it reaches the tissue of the plant whore it undergoes 

 chemical alteration into compounds suitable to build up 

 and repair the waste of the vegetable organism. Into 

 the nature of these most interesting changes, as yet but 

 incompletely mastered by scientific investigators, limit 

 of space forbids us to enquire further. 



The salient feature of our present topic is the relation 

 between the green plant and its carbon-supply. As we 

 have seen, it is enabled by means of the chlorophyll 

 present in the protoplasm of certain of its cells to obtain 

 all that it needs of that most essential constituent of its 

 food from the Carbon dioxide of the atmosphere. This 

 jx)wer is unique, being possessed by no living organisms 

 except such as contain chlorophyll. In the cells of the 

 green plant, as a result of the vital activity of proto- 

 plasm in the presence of chlorophyll are produced organic 

 compounds (proteids) containing Carbon and Nitrogen 

 in such a form that they are available as food *o 

 organisms — plant and animal — destitute of chlorophyll. 

 Among the lower members of the animal kingdom 

 there are numerous in.stanccs of organisms possessing 

 chlorophyll, which therefore subsist partly as plants in 

 that they assimilate Carbon dioxide. As an example 

 may be mentioned the fresh water polype, Ift/dra 

 viridix, familiar to microscopists ; in the cells of whose 

 endoderm are found granules of chlorophyH similar to 

 those of the plant>cell. On the other hand, numerous 

 members of the upper classes of the vegetable kingdom 

 have to some extent thrown off their plant nature and 

 have become partly animal in their tastes and habits. 

 Some of them almost entirely, others to a less extent 

 have lost the character which is most pronounced in 



t Knowxedoe, March, 1900, p. 5S. 



their nearest allies, and havo become destroyers instead 

 of builders up of organic Carbon compounds. These 

 (legrotlcd members of plant society obtain their supplies 

 of organic Carbon from animals or from other plants, 

 living or dead. Of saprophytes (plants which live upon 

 dead organic matter) wc have already said something; 

 it is probable that all plants which flourish in rich 

 humus soils are to somo extent saprophytic. It would 

 take us far beyond our prescribed limits to enter here 

 upon a discussion of the interesting features of the life 

 of a vegetable parasite. It must suflico to mention one 

 well-known example — the " Dodder," of which there are 

 three species in Britain; the " Clover Dodder " {(Uixcuta 

 e pithy iinim. Murr.) is perhaps the best known of these. 

 Its thin wiry leafless stems are destitute of chlorophyll, 

 and are therefore of a dirty yellowish-brown colour. They 

 send short root-like projections into the green juicy 

 stems of the clover from which they derive their entire| 

 nutrinieni,. In clover-fields the nearly circular and ever- 

 increasing brown pat<'hcs caused by the prevalence of 

 this pest over the h\gitimato crop are, in some seasons, 

 but too familiar. There are degrees of parasitism 

 among plants as elsewhere in the organic world. The 

 Dodder is an example of an advanced typo in which the 

 parasite is all but reduced to a condition of absolute 

 dependence. The British Flora contains many plants 

 which rob their fellows of valuable nourishment, but 

 whoso parasitism is less pronounced than that of the 

 Dodder. § Among saprophytic green plants there is a 

 group in which the method of obtaining organic nutri- 

 ment has led to the development of some of the most 

 remarkable forms in the plant world. There are 

 numerous species of carnivorous plants of which a few 

 are represented in our own Flora. Insects are their 

 chief natm-al prey ; and numerous are the devices for 

 capturing them which plants in the course of evolution 

 have adopted. These may bo roughly considered in two 

 divisions. 



A large section of the vegetable carnivora arc 

 provided with chambers or traps into which the 

 animal is allured, and from which it finds escape im- 

 possible. Most interesting examples are seen in two or 

 three species which inhabit the marshes and pools of thij 

 country. The Bladderworts {Utrkularia vulgaris and 

 U. minor) are small rootless plants floating freely in 

 stagnant water. The ordinary leaves are much divided 

 into green thread-like segments. In many places instead 

 of leaves are borne pale-green nearly transparent ellip- 

 soid bladders, which vary in different species from y^ 

 to I inch in diameter. The entrance to the bladder is 

 closed by a valve opening inwards, and is protected on 

 the outside by a tuft of stiff hairs. Only a very small 

 creature such as can crawl in among the tuft of hairs 

 and, pushing in the valve, can pass through a very 

 small orifice, is able to enter. Once inside there is no 

 escape, for the valve fits close and only opens inwards. 

 The bladders which to minute crustaceans, larvae of 

 gnats, and other insects, small worms and other inhabi- 

 tants of stagnant fresh water, possibly suggest refuge, 

 or even food, become chambers of death to those which 

 makr- trial of them. The prisoner is not killed at once, 

 may even live for as long as six days after its capture ; 

 after death the products of its decay arc absorbed by 

 the plant by means of short cells somewhat resembling 

 root-hairs which project into the chamber from its walls. 



X In thp Tcrj- .young condition the Poddcr is not parasitic, but 

 quickly perishes" if it fails to find a suitable host. 

 § Kkowledgb, Mareli, 1900, p. 58. 



