10 Veit Breciier Wfttrock. 



The terminal vegetative cells are also of two kinds: the eonnnon 

 top cells, and the helicoïd cells. The common terminal cells resemble in their 

 form the inclosed cells, with the exception that they have the top conical 

 and rounded. As to their inward construction they agree with the 

 inclosed cells. As long as the individual is increasing in growth they 

 are rather rich in chloroph}^!, but when the increase has ceased, they 

 contain comparativel}^ little chlorophyll. The top cells are the longest 

 cells of the plant. In sterile specimens, where the increase has ceased, 

 the top cell of the principal filament often has a length which is 

 50 — 100 times as great as the thickness (pi. 2, fig. 8). 



Helicoïd cells I name those cells, of which the top is transformed 

 to an affixing organ more or less like a tendril, a helicoïd (from at| = 

 tendril, and eïôog = form). These cells are common only in one species, 

 P. Cleveana nob., but also in the other species of Plthoiihoracea', with 

 the exception of P. mmatrana (v. Mart.) nob. and P. œqualis nob., I have 

 found them now and then. The lower part of the helicoïd cells is 

 generally of a cylindrical form, but their upper part, the helicoïd, is of 

 a very varying shape. In its least developed form the helicoïd cell is 

 unbranched or almost so, and differs then as to shape from common 

 terminal cells only by its upper part, the helicoïd, being more slenderly 

 conical, and not straight, but curved, feeblj^ undulating (pi. 5, fig. 1 h' 

 and 2 A). In normally developed helicoïd cells the top of the cell is 

 ramified in two or more small branchlets. The branchlets of the helicoïd 

 are sometimes almost straight, with only a few small undulating curves 

 (pi. 5, fig. 4); sometimes they are bent like a bow (pi. 5, fig. 5, 7), but 

 most fi-equently they are quite claw-shaped (pi. 5, fig. 6, 11, 12; pi. 1, 

 fig. 18 /(). The contents in the lower part of the helicoïd cell are of the 

 usual nature; in the upper part, or the helicoïd itself, chlorophyll-co- 

 loured protoplasm exists in a quantity so great as to fill this part of 

 the cell almost completelj^ (pi. 5, fig. 4, 6, 7, 10 h). Even if the quan- 

 tity of chlorophyll-coloured protoplasm be not always so great, it is 

 however, as a rule, greater in the helicoïd itself than in the rest of 

 the cell (pi. 5, fig. 1 A, 5, 11, 12 h). A phenomenon which occurs 

 regularly, at least in P. Cleveana nob., viz. that small foreigai particles 

 (grains of humus and other things) adhere to the surface of the • helicoïd 

 (but not to that of the other part of the helicoïd cell), indicates that 

 the cell-membrane of the helicoïd is in some degree of a nature differing 

 from that of the other part of the cell. However, I have neither by 

 optical nor by chemical means been able to gain a more particular 



