170 



ON THE DEVELOPMENT OF THE THECA. 



together : they are often mixed with jointed pellucid filaments, "Jila succulenta " 

 of Hedwig, and in some cases accompanied by the supposed stamens, which in others 

 grow on a different part of the same plant (monoecious), or on a distinct plant 

 (dioecious). Mr. Valentine then states that the object of his paper is chiefly to 

 explain the anatomy of these pistilla, their structure being such as to throw con- 

 siderable light on the sexual theory ; and that he was led to the examination of 

 this subject by discovering the highly curious fact, that the setae of mosses and the 

 Jungermannias terminate downwards in a cone, which is inserted within a corre- 

 sponding cavity of the branch, to which it has but a very slender attachment, or in 

 other words, that the seta has very little if any organic connexion with the plant. 

 This structure appearing to be so anomalous, he determined on the first oppor- 

 tunity to investigate the cause. The following observations are the result of his 

 labours. 



"In the very young state the pistillum contains a single unconnected oval 

 transparent body, or cell, which is situated about one-third from the base. The 

 pistillum as yet has not begun to enlarge, but is of one uniform diameter. The 

 cell is present before the apex of the pistillum has burst open to form the stigma ; 

 and consequently before there is any communication, by means of the tubular 

 style, with the external air. This canal, however, is formed before the bursting 

 open of the apex, and leads directly down to the cell, which appears to be situated 

 in its lower extremity. The cell may be distinguished through the walls of the 

 pistillum with the assistance of a good Wollaston doublet, and I have succeeded 

 in dissecting it out uninjured. It was of a firm texture, a quality depending 

 probably on the thickness of the membrane ; it was also beautifully pellucid, and 

 contained a quantity of moving particles. Upon pressing it with a piece of talc, 

 it burst, and the moving particles escaped. Its diameter was between the one- 

 thousandth and the one-five -thousandth of an inch. Generally one or two only of 

 the pistilla in the same bud arrive at perfection, and the abortive ones are destitute 

 of this cell ; whilst, on the contrary, in Bryum Ugulatum nearly all the pistilla, 

 sometimes amounting to between twenty and thirty, become fruit, and in every one 

 of them may the cell be detected. Bryum roseum very rarely produces fruit in 

 this country, but in winter it not uncommonly possesses healthy-looking pistilla. 

 The manner of the development of this body is exceedingly simple. Soon after 

 the opening of the upper extremity of the style, another cell is formed on the upper 

 ■surface of the first. The two adhere firmly to each other, and may be dissected 

 out together. Presently another cell is formed either on the upper surface of the 

 second, or on its side ; then appears another, and so on gradually increasing in 

 number. When about ten cells are developed the dissection becomes compara- 

 tively easy, and the oblong mass may be exposed, with the original cell still 

 remaining at the base. In this stage it has become rather flattened on the upper 

 surface from the pressure of the newly-formed cells. Whilst this process is going 

 on, the base of the pistillum itself increases in size, not by distention, as is univer- 



