Page:History of botany (Sachs; Garnsey).djvu/363

] the perforation of the walls, believing that the appearances were due to lattice-like thickenings of the cell-walls; he proposed therefore to call Hartig's sieve-tubes latticed cells. Then Nngeli showed in 1861 that in some cases at least there can be no doubt that the walls are actually perforated, and that the sieve-plates serve for the passage of mucilaginous matter in bast-tissue, and the author of this history, it may be remarked in passing in 1863, and Hanstein in 1864, suggested means by which it may be ascertained with certainty that Hartig's sieve-plates are perforated. Meanwhile a number of laticiferous organs had been recognised as forms of vessels in von Mohl's sense, and it was found that such canals are produced by dissolution of the septa of adjacent cells. But the knowledge of the laticiferous organs continued till towards 1865 to be very unsettled and defective, and the examination of resin-passages, and the discovery that they are formed by simple parting of cells from one another, belong to modern phytotomy; Hanstein, Dippel, N. J. C. Miiller, Frank, and others have since 1860 enlarged our knowledge of these forms of tissue. Schacht in 1860 established one of the most important exceptions to von Mohl's view above-mentioned, by demonstrating the formation and true form of bordered pits in the wood of Conifers and in dotted vessels in Angiosperms from the history of their development, and by showing moreover that in all cases where bordered pits are formed on both sides of a partition-wall and the adjacent cells afterwards convey air, there the original very thin partition-wall in the bordered pit disappears, and that consequently in such cases the bordered pits represent so many open holes, through which adjacent cells and vessels communicate. At the same time another hitherto inexplicable phenomenon received its explanation. Malpighi, and after him the phytotomists at the beginning of the present century had remarked, that the large vessels in the wood are not unfrequently filled with parenchymatous cell-tissue, for the origin of which no one could account. The phenomenon,