342 Bibliographical Notices. 



in consequence of the law of development of the plant. We say that 

 the fibres descend, because the middle portion is that which first be- 

 comes distinctly developed into a vascular structure." 



When considering the physiology of vegetation, the author alludes 

 to the function of spiral vessels, and differs from those who look upon 

 these vessels as formed for the special purpose of conveying air. la 

 their earlier developing condition they are full of fluid, and " it ap- 

 pears probable," he says, " that their office, like that of the other vas- 

 cular and fibrous tissue, is to give strength to the parenchyma, and 

 they are peculiarly adapted to the requirements of the tissue in which 

 they are found. Their structure is that which gives the greatest 

 strength and elasticity consistent with lightness. This is a sufficient 

 explanation of their predominance in those parts where the tissue is 

 most delicate and the growth most rapid. The medullary sheath is 

 of course, in this view, regarded as adapted peculiarly to the early, 

 developing condition of the pith." 



The process of respiration and assimilation in plants, according to 

 the author, " consists of the production of a proteine compound, by 

 the agency of light, from the crude juice consisting of water holding 

 in solution carbonic acid and ammonia. When the light is freely 

 admitted to act, as is the case in the usual condition of plants, the 

 assimilating process preponderates in activity over the developing 

 power, and the excess of nutriment not being required for immediate 

 use is deposited as starch instead of cellulose ; the deoxidating pro- 

 cess still continuing, this starch, also receiving in the process a small 

 quantity of nitrogen, becomes chlorophylle. Should the light be in- 

 tercepted now, we shall have a retrogressive series of processes ; the 

 chlorophylle will disappear, since the respiration is reduced to such 

 a low degree that all the carbon is required for development ; the 

 plant continues to grow for a time, its tissues weak and succulent, 

 till all the assimilated carbon having been consumed in the production 

 of new structures, the plant dies of starvation." 

 , The consideration of the reproductive organs and their functions 

 necessarily occupies a large portion of the work, and the morpholo- 

 gical views of structure are brought forward in a lucid and interest- 

 ing manner. After stating the opinions relative to marginal and 

 axile placentation, he concludes thus : — 



" As the question stands at present, we are led to prefer the theory 

 of carpellary placentation by the evidence afforded by the pane^a/ form 

 as occurring in Violacese, Papaveracese, Orobanchacese ; the aiile pla- 

 centas of Scroi)hulariace8e, Ericaceae, &c. appear to admit of an ex- 

 planation by both views, as do also the central placentas of Caryo- 

 phyllaceee. The central placenta of Primulacese and Santalacese 

 favours the idea that the placenta is a prolongation of the axis, and 

 can only be explained by the carpellary hypothesis, by supposing 

 that the central placental column is a confluent whorl of placental pro- 

 cesses developed separately from the carpels through a process of de du- 

 plication." 

 ; The obscure subject of fertilization receives considerable attention. 



