34 



Anatomical Observations on the Elementary Organs of Plants. 



M. Unger* has observed in the genera Helosis and Langs- 

 dorffia extremely thick-sided parenchymatous cells with large 

 and ramified dotted ducts; in Helosis brasiliensis thirteen 

 layers of such thickened cellular walls were enumerated, and 

 in Langsdorffia hypogea even to the amount of thirty layers, 

 which are traversed by dotted ducts, whose diameters mea- 

 sured between O001 7 and 0'0652 ; they are very neatly figured. 

 The ramification of such dotted ducts was however published 

 by me some time previous. M. Unger is of opinion that such 

 thick-sided cells occur in most plants, while I can find them 

 only in a proportionately very small number. Some cases 

 where these thick-walled parenchymatous cells make their 

 appearance under very remarkable circumstances, I will here 

 enumerate. I have observed t that the hard masses of the 

 so-called stories in the inside of pears consist of larger or 

 smaller aggregations of such thick-sided cells, similar to those 

 discovered by M. Mohl in Hoya carnosa. The parietes of 

 these cells increase at times so much in thickness that their 

 cavities almost entirely disappear, and the mass becomes 

 harder than horn and is indigestible. Du Hamel (Book, 

 III. cap. 2.) has already given a very diffuse but elaborate re- 

 port 011 the occurrence of stones in pears. According to him, 

 the stones are diffused through the whole substance of the 

 pear, and their presence is said not to be accidental. The oc- 

 currence of these hard masses is fully discussed by Du Hamel, 

 but in my opinion more elaborately than exhibited in nature. 

 This substance, he remarks, appears to fall into fine white 

 granules which remain somewhat transparent, so that some of 

 the vessels which ramify in them can be observed. Now these 

 fine granules are the simple cells with thickened walls, and 

 the ramified vessels present themselves under modern micro- 

 scopes in the shape of ramified canals in the substance of the 

 cellular parietes. The circumstance of the soft cellular tissue 

 around the hard masses being more or less radiately arranged, 

 is especially worthy of attention. 



* Beitrage zur Kenntniss der parasitischen Gewachse. Annalen des 

 Wiener Museums, ii. p. 38. 



t Neues System der Pflanzen-Physiologie. Berlin, 1837. I. S. 25. 



