512 London Horticultural Society and Garden. 



to be completely rotten at the core. Many persons, seeing it in this 

 state, would have thrown it away as useless ; but Dr. Fischer, who has 

 the direction of the garden, being well acquainted with the laws of vege- 

 table physiology, was determined to try to force the hard outer covering of 

 the Zamia to develope its incipient buds. He had the core carefully 

 scooped out, every particle that was in a state of decomposition being 

 removed, and then filled the cavity with fine rich soil. The bulb was 

 afterwards placed in a moist warm atmosphere ; and he had soon the satis- 

 faction of finding the theory above detailed beautifully illustrated, by the 

 germination of a great number of young plants. 



The manner of the formation of timber (though a subject of such im- 

 portance in a national point of view) is yet involved in considerable 

 difficulties. Many hypotheses have been started, and supported by differ- 

 ent physiologists, but no one has yet been found to which all able men 

 are willing to agree. Professor Lindley owned that he had formed his own 

 opinion on the subject, but, as other opinions were still supported by 

 very scientific botanists, he deemed it his duty to state the principal 

 conflicting hypotheses as clearly and as impartially as he could. He said 

 he had shown in a previous lecture that all trees are either endogenous 

 or exogenous ; that is, that they increase either internally ur externally. 

 The timber trees of England, and of most temperate climates, belong to 

 the latter class; and they increase by concentric layers, formed, one every 

 vear, between the inner bark and the alburnum, or surface of the young 

 wood. The manner in which this layer is deposited is the point respecting 

 which botanists do not agree. Of the various opinions that have been 

 broached on this subject, Mr. Lindley said, he should only state two, which 

 he considered the principal: viz. 1. That the increase in diameter of timber 

 trees is effected by the annual transformation of the inner bark into 

 alburnum ; the former alburnum hardening into wood, and a new inner 

 bark being formed by the exuding juices of the tree : and, 2. That fibres 

 are being constantly sent down by the leaves, which imbedding themselves 

 in the cellular tissue, formed by the descending sap, make a new layer 

 between the inner bark and the alburnum. 



Various experiments have been tried by the supporters of the first of 

 these opinions ; one of which seemed almost conclusive. A portion of 

 the outer bark having been removed, and a thin plate of silver having been 

 bound on the outside of the inner bark, this plate of silver was, in a few 

 years, found buried in the tree. On the other hand, the advocates of the 

 second hypothesis, viz., that the layer of new wood is formed by deposi- 

 tions from the leaves, assert, that, if a tree be ringed to such a depth as to 

 cut off the communication between the alburnum and the leaves, the stem 

 below that ring will not increase in size, but that the part above the 

 division will exhibit an extraordinary swell, as though the nourishment 

 intended for the whole trunk were concentrated to that point. In further 

 support of the same hypothesis, it had been observed that trees planted 

 on the edge of a wood, in such a situation as to have only one side 

 exposed to the full benefit of the sun and air, and which, of course, 

 have partially developed their leaves and branches, are found invariably 

 to have their concentric layers of wood broader on the vigorous than on 

 the stunted side. After stating these opinions, Mr. Lindley observed that 

 many objections had been raised to the second of them, because its first 

 supporters had asserted that each individual leaf, or rather bud, sent down 

 fibres through the whole body of the tree directly to the ground. This 

 appeared to be carrying the doctrine rather too far. 



