712 Mr. Brown on the Organs and Mode of 



This nucleus of the cell is not confined to Orchideae, but is 

 equally manifest in many other Monocotyledonous families ; 

 and I have even found it, hitherto however in very few cases, 

 in the epidermis of Dicotyledonous plants ; though in this 

 primary division it may perhaps be said to exist in the early 

 stages of development of the pollen. Among Monocotyledones 

 the orders in which it is most remarkable are Liliaceae, Heme- 

 rocallideae, Asphodeleae, Irideae, and Commelineae. 



In some plants belonging to this last-mentioned family, espe- 

 ciallj'^ in Tradescantia virginica and several nearly related spe- 

 cies, it is uncommonly distinct, not only in the epidermis and in 

 the jointed hairs of the filaments*, but in the tissue of stigma, 



in 



* The jointed hair of the filament in this genus forms one of the most interesting 

 microscopic objects with which I am acquainted, and that in three different ways : 



1st. Its surface is marked with extremely fine longitudinal parallel equidistant lines 

 or striae, whose intervals are equal from about l-15,000th to l-20,000lh of an inch. 

 It might therefore in some cases be conveniently employed as a micrometer. 



2ndly. The nucleus of the joint or cell is very distinct as well as regular in form, and 

 by pressure is easily separated entire from the joint. It then appears to be exactly 

 round, nearly lenticular, and its granular matter is either held together by a coagulated 

 pulp not visibly granular, — or, which may be considered equally probable, by an en- 

 veloping membrane. The analogy of this nucleus to that existing in the various stages 

 of development of the cells in which the grains of pollen are formed in the same species, 

 is sufficiently obvious. 



Srdly. In the joint when immersed in water, being at the same time freed from air, 

 and consequently made more transparent, a circulation of very minute granular matter 

 is visible to a lens magnifying from 300 to 400 times. This motion of the granular fluid 

 is seldom in one uniform circle, but frequently in several apparently independent threads 

 or currents: and these currents, though often exactly longitudinal and consequently in 

 the direction of the striae of the membrane, are not unfrequently observed forming va- 

 rious angles with these striae. The smallest of the threads or streamlets appear to 

 consist of a single series of particles. The course of these currents seems often in some 

 degree affected by the nucleus, towards or from which many of them occasionally tend 

 or appear to proceed. They can hardly however be said to be impeded by the nucleus, 

 for they are occasionally observed passing between its surface and that of the cell ; a 



proof 



