208 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
even of two well differentiated generative zones. The permanent tissues 
of the stem of Monocotyledons are rarely formed in the primitive 
meristem ; in their formation a part is usually taken by the secondary 
meristem produced by one or both of the cambial zones. The order of 
formation of the bundles is sometimes strictly centrifugal, but more 
often they make their appearance in the stem in centripetal sequence ; 
or mixed types are formed by a combination of the two. No primary 
cortex, consisting of a layer of tissue distinct from the embryonic con- 
dition, exists in the stem of Monocotyledons. When the leaves have a 
sheathing character, the cortex of the stem is, in its origin, simply a 
prolongation of the tissue of the foliar sheaths. 
Anatomy of the Aquatic Gentianacese.* — M. E. Perrot gives a 
general account of the peculiarities of structure of the genera Menyantlies, 
Neplirophyllidium, Villcirsia, Limncintliemum, and Liparophyllum, making 
up the tribe Menyanthoideao of Gentianaceas. The vascular bundles are 
collateral, without internal phloem ; the secondary xylem is absent, or 
but feebly developed ; in the latter case it is composed of scalariform 
vessels ; sclerites occur in nearly all of the species ; the mesophyll is 
bifacial ; the stomates are formed simply by the division of an epi- 
dermal cell ; the mechanical tissue is scanty ; there is but little starch, 
except in the endoderm ; crystals of calcium oxalate do not occur. 
Sieve-Tissue outside the Phloem and Vascular Tissue outside the 
Xylem.| — In certain species of Gentianacese belonging to the genera 
Gentianci and Sivertia, M. E. Perrot finds, in the root, sieve-fascicles 
within the xylem, resulting from the segmentation of one or more cells 
of the secondary xylem-parenchyme. In the stem there are always 
sieve-fascicles in the pith, especially in its periphery, but sometimes 
throughout its whole extent. Some species have sieve-islands within 
the xylem ; others possess in the pith, in addition to the sieve-fascicles, 
cribro-vascular bundles, the vessels of which are simply tracheae. In the 
leaf are peri medullary sieve-fascicles proceeding from the stem, and 
strongly developed in the periderm of the bundles of the veins. 
Effect of JEcidium elatinum on Abies balsamea. J — Mr. A. P. 
Anderson has studied the anatomical changes which are the result of the 
“ witch-broom ” produced on the balsam pine by the attacks of JEcidium 
elatinum. There are fewer stomates on the diseased leaves, but their 
distribution is normal. The hypodermal strengthening cells are more 
irregular in form and size ; they are often found in nests and groups. 
Transfusion-tissue is nearly always present, often in from one to three 
small areas on the dorsal side of the phloem. The diseased buds are 
covered with a greater number of bud-scales, which are smaller than the 
normal ; they are covered by resin in the winter, and are fringed with 
marginal hairs. Resin canals are fewer in the diseased scales, but are 
always present in the wood of the tumour, and nearly always in the 
wood of older diseased branches above the tumour ; resin vesicles begin 
to form even in diseased shoots of the first and second year. Epidermal 
* Bull. Soc. Bot. France, xliv. (1897) pp. 340-51 (1 pi.). Cf. this Journal, 1897, 
p. 405. 
f Comptes Rendus, cxxv. (1897) pp. 1115-8 ; Jouin. de Bot. (Morot), xi. (1897) 
pp. 374-90 (1 pi. and 6 figs.). J Bot. Gazette, xxiv. (1897) pp. 309-44 (2 pis.). 
