Meyen's Report for 1839 on Physiological Botany. 131 



lieves that this is as it were the commencement of the forma- 

 tion of partitions, which are observed to appear in Conferva, 

 &c. for the increase of the cells. I cannot agree to this hy- 

 pothesis, for these partitions are formed in quite a different 

 manner, and the appearance of a partition by which the cy- 

 closis within a utricle is divided into two parts is quite an 

 accidental and rare pheenomenon. I myself observed it in the 

 Chara in 1825 (Linnaea, 1827, p. Q(y), and saM' that thereby 

 two streams were produced, which lasted until the obstruction 

 was carried away. M. Morren observed spiral fibrous cells 

 of various forms in the enlargements of the base of the stalk 

 of this new Malaxis. 



M. Morren* has published an interesting paper ' On the 

 Discoid Pith of Plants,' which had been observed by Grew in 

 Juglans regia, by M. Mirbel in Nyssa aquatica and Pliyto- 

 lacca decandra, as well as by DeCandoUe in Jasmlnum offici- 

 nale. M. Morren thinks it very probable that this structure 

 of the pith may occur in many other plants ; he himself found 

 it in plants belonging to the families Santalace(e, Juglandece, 

 Phytolacce(B,Jasmine(2, and Bigno?iiace(e; but he remarks, that 

 some species of a genus exhibit this formation, while others 

 do not. The figures which accompany this treatise of M. Mor- 

 ren were drawn from Begonia argyrostigma, Juglans regia, 

 Jasmimimf ruticans, and P/iytolacca decandra ; the pith in these, 

 as in many other plants, exhibits in the earlier periods of 

 growth a homogeneous mass of cells, in which, finally, more 

 or fewer horizontal clefts (slits) make their appearance. These 

 slits are placed in regular order above one another ; they in- 

 crease gradually, and are finally separated merely by mem- 

 branous dissepiments. M. DeCandolle believed that these ca- 

 vities arose from a rupturing of the cellular tissue caused by the 

 extension produced by the growth of the plant ; but M. Morren 

 has shown that they arise from a regular separation of the 

 cells, and are therefore to be compared to the air-passages. 



Mr. Patrick Keithf has made some observations on pith, in 

 order to settle the two following questions : — 1st, Does the pith 

 appear in any part of the root ? and 2ndly, Are the dimen- 

 sions of pith changed after it is once fully developed ? With 

 respect to the first question, observations made on the roots 

 of young plants of Acer jiseudojilatanus, Fagus sylvatica, and 

 Coryhts Avellana, showed him that the principal root is also 

 furnished with pith. The second question Mr. Keith answers 

 by the examination of a three-year-old ash stem which was 



* On the Discoid Pith of Plants, Ann. of Nat. Hist., Oct. 1839, p. 73-88. 

 I Of the Pith of Plants, Ann. of Nat. Hist., Ap. 1839, p. 77. 



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