70 ON THE VASCULAR TISSUE OF PLANTS. 



inner surface of the cylindrical cell containing them ; and it appears 

 that this direction can be in most instances resolved into the spiral form, 

 even in those vessels in which when the fibre is perfect that form is lost 

 from changes that have occurred since the primary deposit of the 

 granules.* 



The singular law of the spiral arrangement of the granules was 

 mentioned as deserving some attention, being sometimes arranged in the 

 direction of a right-handed screw in other cases in the opposite man- 

 ner ; sometimes in a single screw in others as a compound one ; many 

 fibres running to constitute the helix. It was considered not improba- 

 ble that these granules possessed certain polarities, and that also the 

 usual continued passage of electrical currents through the axis and 

 branches of a plant may possess the power of determining the linear 

 and spiral order of floating granules, somewhat as the electrifying of 

 the particles of gold-leaf mixed with water causes them to assume a 

 linear condition ; but there can be no doubt that much in this matter is 

 effected by the agency of the vital powers of the cell itself, controlled 

 by the influence of the plant. 



It had been conjectured by Schleiden (whose observations the paper 

 was intended in a great measure to confirm) that a current existed 

 between the gelatinous contents of the vessel and its wall, which pre- 

 ceded the formation of the fibre within, and gave to it the direction it 

 afterwards took. This opinion was shewn to be not altogether correct, 

 by the fact that the granules become separately attached to the inside 

 of the vessel without any discernible distance from each other, begin- 

 ning first at one end and proceeding gradually to the other ; occasion- 

 ally a vessel being found, in which part had the granules laid down in 

 the spiral direction, and the other as yet without any adhering to the 

 membrane, the fibre elongating like a root by the materials for its 

 increase being added always to the growing point. 



The granules so attached, becoming nourished by the contents of the 

 vessel, have the moniliform appearance they first present in a short 



* The author, at the period of reading this paper, had examined several specimens 

 of plants in which it appeared that the spiral form was not peculiar to all, and that 

 the granules were sometimes deposited at the commencement in the manner in which 

 the fibre was found ultimately to obtain. This induced him to mention in the 

 original paper, that each vessel had a peculiar arrangement of the granules for 

 itself; but subsequent observations have led him to believe, that the spiral form 

 more or less perfect is the type of all, which opinion is entertained by other vege- 

 table anatomists. 



