Monotropaceae with Reference to Ericaceae 63 



four small areas of xylem. These patches consist only of 1-3 

 cells, generally reticulate tracheids, no vessels being present 

 according to Kamienski. Drude reports the presence of spiral 

 vessels. The writer has not seen any of the latter. Within 

 the small circle formed by these four xylem elements occurs 

 a parenchymatous mass of pith. Between and outside of the 

 xylem patches is a comparatively large amount of phloem, 

 composed of thin-walled cells, a few sieve tubes with slightly 

 thick walls being present. These sieve tubes are described by 

 Kamienski as having no true sieve plates, but that these are 

 replaced by transverse partitions, and that the walls are thin 

 at certain points. They are easily distinguished by their more 

 granular contents. Secondary thickening occurs; Kamienski 

 states that no cambium is present, and that the secondary 

 tracheids are disposed either singly or in groups toward the 

 pith or sometimes away from the pith. The phloem also grad- 

 ually increases in the number of cells, until they join to form a 

 ring around the wood. Queva (62), on the other hand, de- 

 scribes the secondary wood as being formed only in a centrif- 

 ugal direction — outside of the primary tracheids — and that 

 after this, cambial arcs form and produce a continuous ring of 

 xylem and phloem. Older roots examined by the writer showed 

 an increase in the number of xylem elements and between the 

 xylem and the phloem a layer of thin-walled cells resembling 

 a cambium. The roots were not old enough to show the con- 

 tinuous ring of xylem and phloem described by Queva. 



No complete description of the old root of M. uniflora has 

 been found by the writer. The epidermal cells become filled 

 with hyphae, but do not appear to drop off as soon as in M. 

 hypopitys. The mycelial sheath still surrounds the oldest part 

 of the root. The fibrovascular cylinder has a very irregular 

 distribution of elements. The 3-4 single tracheids in young 

 roots have increased in number, until there is quite a large area 

 of wood, mostly reticulated tracheids. The secondary growth 

 in thickness, from the material examined, seems to occur in 

 the manner described by Queva for M. hypopitys. 



In the least saprophytic ones the epidermis soon dies and 

 falls off, carrying with it the fungal hyphae as in Chimaphila 

 and Pyrola. In Monotropa and especially M. uniflora the 

 epidermis is still living and filled with hyphae when the root 



