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fined to the extremities of tbeir roots — the spongioles, as a means of obtaining food. 

 These spongioles are placed in the soil, and from the soil, and from no other source, 

 do they derive their water and carbonic acid. It is this that makes carbonaceous soils 

 so valuable when any agent is added to them that will facilitate the union of their 

 carbon with oxygen, and thus supply to plants an abundance of carbonic acid. On 

 the necessity of water as a food for plants I need not dwell ; and that this alone enters 

 plants from the soil is proved by the flourishing vegetation of a swamp during a drought, 

 compared with the withered aspect of the same on hills and well-drained fields. But 

 water and carbonic acid are by no means the only food of plants; there are other mat- 

 ters which they derive from the soil, and which they cannot get from any other source. 

 The various saline and earthy constituents of plants are derived from the soil ; and 

 unless these are supplied the plant perishes. The nature and proportion of these vary 

 very considerably in dilFerent families, but in most cases they are essential, if not to the 

 existence, at least to the health and productiveness of the plant. Of these substances 

 the phosphates, nitrates and carbonates of lime, potassa and soda, silica and ammonia, 

 may be given as examples. It is a knowledge of this fact that is now giving such an 

 impetus to the enquiry concerning the manuring of plants, and which, far from lead- 

 ing to the conclusion that the composition of the soil is of little importance, attaches 

 to it the utmost value. For this purpose the vegetable physiologist has called in the 

 aid of the chemist ; and Dr. Daubeny, at a late meeting of the Agricultural Society, 

 presented a plan for keeping a debtor and creditor account between the soil and plants 

 that grew on it, seeing that the latter took away that which the former possessed. It 

 is a knowledge of this fact that gives the true theory of the rotation of crops, the ne- 

 cessity for which does not arise from the excretions of a plant being poisonous to itself 

 and not to another, but from the fact that plants abstract from the soil the whole of an 

 ingredient that, as food, is necessary for their health ; this is not supplied till after the 

 next manuring. That the earth supplies ingredients necessary to the existence of 

 plants, is also proved by their distribution on the surface of the globe, independent of 

 height, of heat and light, which are so important; some plants grow on one stratum 

 and some on another ; and many plants are known to geologists as determining the 

 existence of particular rocks, whose particles are mingled with the soil. I cannot 

 therefore admit that the earth is " simply a receptacle for roots,'' for the very constitu- 

 ents of which the earth is composed, are constantly undergoing decomposition and en- 

 tering into the structure of the plant ; and had not the earth naturally or by artificial 

 means a peculiar constitution, the plants which grow on it could not exist. — JEduin 

 Lankester ; 43, Hart Street, Bloomsbmy, May 6, 1842. 



158. Note on Sagina apetala and maritima. In the numerous examples of Sagina 

 apetala which I have witnessed, I have never failed to detect rudimentary petals, (see 

 ' British Flora '). This obtains also in the maritime variety found in Anglesea, near 

 Beaumaris. S. maritima is strictly apetalous. The latter species I have never seen 

 growing at WaiTington : the nearest habitat known to me is Runcorn Gap, on the 

 Mersey. — W. Wilson ; Warrington, May 6, 1 842. 



159. Carex tenella, (Phytol. 128). A word on this subject. I have no doubt that 

 the figure of Schkuhr has been seen by the author of ' British Flora,' and I think there 

 is good evidence of its having been consulted at the very time when that part of the 

 ' British Flora ' was written. The mistake, if any has been made, may even have been 

 caused by relying too implicitly on Schkuhr's figure of the ripe fruit. This, in Sir J. 

 E. Smith's opinion, has been taken " from a starved specimen of C. loliacea,''^ which 



