Plant- Grozaih. 131 



Except iu the instance related, I have never met with dry-rot and wet- 

 rot in the same tree ; neither have I met with dry-rot and touchwood side 

 by side in the same tree : but nothing is so common as to find oaks attacked 

 by dry-rot in their trunk or in some large branch, while their small 

 branches ,\re being turned to touchwood, and strew the ground. 



Correspondence is invited on this subject — [^t/. J. F.'] 



Plant-Growth. 



Me. W. T. Thiselton-Dyer, M.A., Assistant Director, Royal Gardens, 

 KeAv, lectured on March 2Gth, at the London Institution, on " Plant- 

 Growth and its Present Problems." He said Linnaeus, in a celebrated 

 definition, had attributed growth to each of the three kingdoms of nature. 

 Mr. Dyer then pointed out the distinction between the mere acceptiou 

 exhibited by a crystal and the " intussusception " of new material which 

 was characteristic of plants and animals. This was the result of what was 

 known as their cellular structure, the history of our present knowledge of 

 which was then traced. It Avas due, in the first place, to two former 

 secretaries of the Royal Society — Robert Hooke and Xehemiah Grew, — 

 who in the latter part of the seventeenth century clearly made out the 

 fact that plants were made up of the units of structure, which they 

 called bladders or utricles, and which are now called cells. Hooke's 

 observations were made on a familiar substance, cork, the true structure 

 of which he accurately described ; but Grew's investigations, spread over 

 a much wider field, were, with the appliances at his command, prac- 

 tically exhaustive, and were wonderfully accurate even in the light of 

 present knowledge. They were also thoroughly confirmed by the con- 

 temporary researches of Malpighi made at Bologna, the publication of 

 whose observations was only preceded by a few months by that of Grew. 

 During the eighteenth century investigation in this subject proceeded along 

 lines altogether erroneous. The want of a correct understanding of animal 

 structures, and the desire, in itself laudable, to recognise a unity of plan of 

 organization in the two kingdoms, led to the view that plants were made 

 up of fibres and thin plates. Wolff (who anticipated the poet Goethe in 

 his discovery of the true relation of the parts of flowers) was no less at 

 fault in imagining that plants were ' composed of a uniform material 

 excavated into minute cavities and canals : some survival of this view exists 

 even to the present day. With the commencement of the present century 

 a fresh start on the true track Avas made, and once more in England. The 

 accurate description by the celebrated botanist, Robert Brown, of the 

 minute body contained in cells, and known as the nucleus, and as to 

 the function of which at the present moment the most important re- 

 searches are in progress, attracted attention to the cell as the true unit 

 of structure. The cell theory, as it was called, received in the course 

 of a few years a complete development in the hands of Schwann and 



