542 



THE SOUTHERN PLANTER. 



of the most ancient, in which we see fixi- 

 ty so strikingly marked under such very 

 different external conditions. In this sec- 

 ond part of my discourse I have directed 

 attention to the importance of physiology 

 in reference to races. The subject of races 

 is one which belongs particularly to physi- 

 ology as distinguished from organic chem- 

 istry ; as also does the constitution of spe- 

 cies or kinds of plants, of which I have 

 previuusly spoken. 



The third head of my lecture has refe- 

 rence to the constitution of particular or- 

 gans. No organ, perhaps, is of more in- 

 terest in this respect, or presents a greater 

 variety of conditions, having relation to 

 practice, than the root. It is very much 

 the case with those who take merely a 

 chemical view of physiology, to regard the 

 root as a kind of absorbing machine, as a 

 process of prolongation of the structure 

 into the soil (serving like the lower part 

 of the wick of a lamp) to absorb the nour- 

 ishment contained in the soil. Such a 

 view as this is a very partial view of the 

 nature of the root, and leaves out of con- 

 sideration the most important of its physi- 

 ological characters. In the first place, 

 roots are very different in their kinds. — 

 We have two kinds of roots among the 

 flowering plants, examples of which occur 

 among commonly cultivated plants. We 

 have roots such as are produced by the 

 turnip, by the bean, and various legumi- 

 nous plants; and we have roots produced 

 by the different kinds of grass and grain 

 plants, where there is an original differ- 

 ence in the structure, a difference depend- 

 ing on the modes in which they first sprout 

 from their seed. One class produces a 

 large root; the class to which the turnip 

 and bean belong produces a main trunk, a 

 continuation of the lower part of the stem, 

 from which the different absorbing branch- 

 es are given off as the branches are from 

 the trunk above. In the grass and corn 

 plants there is never any main tiunk of 

 that kind produced, but a variable number 

 of fibres or filaments thrown out from the 

 bottom of the stem, as we see from the 

 bottom of a Hyacinth bulb when growing 

 in a glass. The number of these and their 

 vigour depend greatly upon the stimulus 

 applied lo the plant at the base of the 

 stem when the roots are sprouting. The 

 number is not fixed in any given plant ; 

 it varies to a great extent in proportion to 



the supply of food furnished to the plant. 



But when developed in either of these 

 ways, plants do not all send their roots at 

 once into the soil to absorb the food in the 

 same way. We have ordinary plants 

 growing down into the soil ; then we have 

 a large class growing in water ; and in ad- 

 dition to these there are others which 

 never make their way into the earth or 

 into the water, but are supplied by the 

 moisture contained in a damp atmosphere. 

 Considerable difference must necessarily 

 exist in the way in which these plants ab- 

 sorb 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 

 unfrequenlly find Clover fields in this 

 country infested by a vegetable parasite, 

 of which the plant before me is a speci- 

 men, having brownish withered-looking 

 stalks apparently destitute of leaves (the 

 leaves being represented by scales), and 

 terminating in pale brawnish flowers. — - 

 These flowers are as perfect as that garden 

 Snapdragon, or the Foxglove, to which 

 they are nearly allied, and they produce 

 seed as perfectly as ordinary plants with 

 proper leaves and well-developed struc- 

 tures. 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 organi- 

 cally connected. The germination of these 

 plants has been observed. When 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 para- 

 sitic, they wither away; if they find a 

 plant of the kind in the neighbourhood 

 they send their slender rootlets into the 

 root of the plant which they are about to 

 infest, and very soon the structures be- 

 comes completely grafted, after which the 

 plant derives the whole of its nourish- 

 ment from the root of the plant which it 

 has attacked. Not only have these plants 

 a particular constitution, but they infest 

 particular species or groups. This small 

 Broom (Orobanche minor) infests Clover, 

 another kind infests Ivy, another kind in- 

 fests bed-straw ; six or eight different spe- 

 cies are known to botanists of this coun- 

 try, and many more in foreign countries. 

 This plant is an illustration of a peculiari- 

 ty in the constitution of roots upon which 

 depends the peculiarity of the entire plant. 



