THE FARMER'S MAGAZINE. 



moisture contained in a damp atmosphere. Considerable 

 difference must necessarily exist in the way in which these 

 plants absorb their food ; and not only is this the case, but we 

 have plants which do not absorb their food from the soil or 

 from any mineral sources. For example, we do not iiufre- 

 quently find Clover fields in this country infested by a vej^e- 

 table parasite, of which the plant before me is a specimen, 

 having brownish withered-looking stalks apparently destitute 

 of leaves (the leaves being represented by scales), and termi- 

 nating in pale brawuish flowers. These flowers are as perfect 

 as that garden Snapdragon, or the Foxa;love, to which they are 

 nearly allied, and they produce seed as perfectly as ordinary 

 plants with proper leaves and well-developed structures. This 

 plant will be seen to be firmly attached to the Clover — indeed 

 when the sections are placed under a microscope the two 

 structures are found to be organically connected. The germi- 

 nation of these plants has been observed. AVhen the seeds are 

 sown they sprout in the ordinary way ; but if they do not find 

 a plant of the kind upon which they are naturally parasitic, 

 they wither away ; if they find a plant of the kind in the 

 ueighbourhood they send their slender rootlets into the root 

 of the plant which they are about to infest, aud very soon the 

 structures become completely grafted, after which the plant 

 derives the whole of its nourishment from the root of the plant 

 which it has attacked. Not only have these plants a particular 

 constitution, but they iufest particular species or groups. This 

 small Broom (Orobanche minor) infests Clover, another kind 

 infests Ivy, another kind infests^bedstraw ; six or eight dif- 

 ferent species are known to botanists of this country, and many 

 more in foreign countries. This plant is an illustration of a 

 peculiarity in the constitution of roots upon which depends 

 the pecularity of the entire plant. It is a plant interesting to 

 agriculturists, not on account of any beneficial results, but on 

 account of the mischief which it does. I have also here a 

 specimen of the Dodder (Cuscuta), which has been so mischiev- 

 ous occasionally also in Clover fields, particularly in Norfolk, 

 The plant has flowers like the Convolvulus on a small scale ; 

 it belongs to the family of the Convolvulaceaj, the same family 

 to which belongs another pest, the Bearbind. This plant 

 forms perfect seeds like the seeds of the Convolvulus, and the 

 flowers are in all respects as complete as the flowers of that 

 plant. When the seeds fall to the ground they germinate like 

 ordinary seeds, they stretch out along the ground in a little 

 narrow wire-like pr6cess, and if that does not meet with 

 a clover plant it dies ; but if it finds the clover plaut, it makes 

 its way to it, and the older part of the original root soon 

 withers away. The part of the stem which is attached to the 

 clover produces little papilla or peg-like processes of a delicate 

 structure, which drive their way iuto the tissue of the stalk of 

 the clover. The plaut derives the whole of its nourishment, 

 after the first early epoch of its growth, from the juices of the 

 f lant which it infests : the plants are entirely parasitic. But 

 tuc modifications of parasitism by means of roots are not ex- 

 hausted by such plants as broomrapes and dodders; for we 

 have others which are imperfectly parasitic, and which have in 

 this kind of parasitism a distinct constitution. Of these are 

 the weeds often found in pastures, called the Eye-bright, the 

 Yellow-rattles, and some others. I have before me a specimen 

 of a Thesium, a plant also belonging to this class, which is 

 rather rare in this country. The roots at first attach them- 

 selves to other plants liks the broomrapes. A careful 

 examination shows little suckers or disc-like processes upon 

 the roots ; but when the plant obtains a certain degree of 

 vigour it ceases to be parasitic, it cease? to depend upon the 

 nurse, throws up a stem, becomes covered with green leaves, 

 and provides for its own sustenance. The Mistletoe is an ex- 



ample of parasite where the root ceases to exist at a very early 

 stage of growth. When it germinates it produces a rootlet 

 like any other seed. It attaches itself to the branches ot the 

 trees it infests by the viscid gummy or mucilaginous matter 

 surrounding the seed. If it falls upon an old branch covered 

 with a corky bark it will germinate, but nothing more; but if 

 it falls upon a young shoot covered merely by a delicate thin 

 rind and sticks there, when it begins to germinate the lower 

 part of the stem spreads out to a kind of disc, and from the 

 centre. This the Utile rootlet penetrates through the spongy 

 parts beneath the bark, making its way to the cambium, where 

 the new growth of the nurse-plant will take place, so tliat the 

 seedling is brought exactly to the same condition as a bud 

 when it is grafted on tlie stock in the ordinary operations of 

 gardening ; an organic couuection is set up, the tissues 

 become vitally connected, aud then the plant becomes, as it 

 were, a branch of the nurse-plant, and no longer produces any 

 root structure. Still, though it has no root, unlike the broom- 

 rapes to which I have adverted, it does produce green leaves ; 

 even its stem becomes green ; aud it decomposes oxygen; there- 

 fore, though it does not absorb its own food, it performs some 

 part of the processes of vegetation, and takes a share in the 

 elaboration of the food. These are interesting cases of peculiar 

 constitutions in plants, manifesting themselves in peculiar 

 vital qualities, as they may be fairly called, in the roots. It 

 certainly must be regarded as a vital peculiarity in these plants 

 that they attach themselves in this way not merely to other 

 plants, but to particular parts and even to particular species 

 of plants. 



In preparing this lecture, I have noted down in re£,ard 

 to this subject some facts and conclusions as to the functions 

 of roots generally in reference to the supposed phenomena 

 of choice. The above are illustrations of what may be 

 called in roots a choice of food, and they may be taken as 

 serving, in part, as evidence on the general question. But 

 we must not regard this kind of choice in the same way that 

 we regard choice of food in man, for example. The plant 

 cannot go and seek out what food it pleases, but it has a 

 kind of negative choice. It cannot grow upon food that is 

 unsuitable ; it must have that food which is suited for its 

 particular constitution. If the food is indifferent, the plant 

 will notgrow, but need not be absolutely injured. If the 

 food is noxious, the plant will be killed by it, but to grow 

 properly it must have food which is favourable ; so that we 

 may say there is a kind of choice, which, as already re- 

 marked, is as it were negative. It has the power of refusing 

 to grow unless proper food is supplied. That is the only 

 way in which we can suppose that plants have really a 

 choice. I think this statement is sufficient to explain many 

 of the phenomena which have been brought forward, as tend- 

 ing to prove the existence of choice food in plants. The 

 circumstance that a fair supply of food favourable to the 

 plant exists in the soil is sufficient to account for the plant 

 possessing abundance of that particular substance in its ash, 

 and a greater abundance of that substance in its ash than 

 another plant whose constitution does not require that par- 

 ticular kind of food, and which has been well developed 

 in a different soil. In addition to this refusal to produce 

 organization out of unfit food, we have certain phenomena 

 which are partly chemical and partly physical. The absorp- 

 tion of the root depends to a great extent upon what is 

 called endosmosis — the power of the membrane of the I'oot- 

 lets to draw in fluids and solutions by which the root is sur- 

 rounded with a certain amount of force, arising in many 

 cases simply from the fact that the fluids within are denser 

 than those without. But decompositions probably take 



