54 PROFESSOR THISELTON DYER. 



bundles in consequence is shown in fig. 3 in the plate 

 accom})anying this paper. The strings of crystal-hearing 

 cells are relatively most ahundant in the peripheral bundles. 

 They are always confined to the exterior of the bundles, 

 and do not occur elsewhere in the stems. Under the mi- 

 croscope the crystal-bearing cells are a very conspicuous 

 feature in a longitudinal section, especially when it happens 

 to graze the surface of the bundles tangentially. Cells in 

 linear strings, somewhat similar, only without crystals, and 

 usually not isolated, occur in the interior of monocotyledo- 

 nous fibro-vascular bundles, and avouUI then be termed cam- 

 biform. The outside of the bundles appears to be a very 

 anomalous position for them ; indeed, I know of no similar 

 instance of such an arrangement, and the presence of a 

 crystal in each cell makes it still more remarkable. 



The crystal-bearing cells being gi-ouped in strings, which 

 run parallel Avith the bundles, seems to indicate that the crys- 

 tallizable matter is either conveyed directly or in its constitu- 

 ents more readily along their course than in any other direc- 

 tion. Sachs has shown that the fibro-vascular bundles in the 

 active parts of plants have, when fresh, an alkaline reaction, 

 while the adjacent parenchyma is acid. This alkaline reac- 

 tion is connected, as is supposed, with the transport through 

 them of nitrogenous protoplasmic matters. Cambiform cells 

 seem always to take an active part in such transmission. One 

 may, perhaps, hazard the theory that in Pandanus the cam- 

 biform cells occur on the exterior instead of the interior of 

 the bundles. They are, therefore, especially liable, as their 

 proper functions draw to an end, to the invasion of the acid 

 fluids of the general parenchyma ; crystalline salts are, con- 

 sequently, formed from the mixture of these fluids Avith their 

 basic contents. It can hardly be supposed that the end and 

 object of the cells is to hold the crystals. It seems more 

 reasonable to think, on the contrary, that the formation of 

 crystals commences only when the original functions of the 

 cells are bee-inning to cease. It should be remarked, in 

 connection with this, that their walls are clearly thickened, 

 / and almost adhere to the contained crystals, but they do not 

 seem to have any pores. 



Crystals of an oblong prismatic form do not occur except 

 in connection with the bundles in any of the tissues of 

 Pandanus ; as, however, noticed by Gulliver,^ raphides 

 abound in the leaves and " bark." I have found them plen- 

 tifully dispersed in the general parenchyma of the stem, 

 though in greatest abundance nearest the rind. They are 

 » ' AuD. aud Mag. Nat. Hist.,' v. xiii, 293 ; v. xvi, 333. 



