IN ORCllIDK/E AM) ASCLEPIADEiE. 513 



impregnation ; and in tlie latter state the utriculi arc 

 marked with from one to three areolcC of similar appear- 

 ance. 



The nucleus may even be supi)ose(l to exist in the pollen 

 of this family. In tlic early stages of its formation at 

 least a minute areola is often visible in the simple grain, 

 and in each of the constituent parts or cells of the com- 

 pound grain. But these areola3 may perhaps rather be 

 considered as merely the ])oints of production of the tubes. 



This nucleus of the cell is not confined to Orchideae, 'j^- 

 but is ecpially 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 Liliacea^, Hemerocallidea^, Asphodeleae, 

 Iridea\ and Commelinea\ 



In some plants belonging to this last-mentioned family, 

 especially in Tradescanila virfjinka and several nearly 

 related species, it is uncommonly distinct, not only in the 

 epidermis and in the jointed hairs of the filaments,^ but in 



' The jointed hair of tlie filament in this genus forms one of the most 

 interesting microscopic objects with wliich I am acquainted, and that iii tliree 

 different ways : 



1st. Its surface is marked with extremely fine longitudinal parallel equi- 

 distant, lines or striae, whose intervals are equal from about 1-1 5,000th to 

 l-20,000lli of an inch. It might therefore in some cases be conveniently em- 

 ploy ed as a micrometer. 



2n(ily. 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 

 a|)pcars to be exactly round, nearly lenlicuhir, and its granular matter is either 

 held together by a coagulated pulp not visibly granular, — or, which may be 

 considered equally probable, by an enveloping membrane. The analogy of this 

 nucleus to that existing in the various stages of development of tlie cells in 

 which the grains of pollen are formed in the same species, is sufficiently 

 obvious. 



3rdiy. 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 n)agnil'ying from 300 to 100 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 slriie 

 of the membrane, are not unfrequcntly observed forming various angles with 

 these strice. The smallest of the threads or streamlets appear to consist of a 



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