210 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
(3) Structure of Tissues. 
Apical Tissue in the Stem of Phanerogams.* — M. H. Douliot finds, 
from an examination of the stems of species belonging to about 20 genera 
of Gymnosperms (Abietinem, Cupressinem, Taxineee, and Gnetacem), 
that the stem always grows, like that of Vascular Cryptogams, by means 
of a single apical cell, which is sometimes pyramidal, sometimes prismatic. 
It differs also from that of Monocotyledons and Dicotyledons in the 
absence of an independent epiderm. Among the 23 Monocotyledons 
examined, he finds two types, viz. (1) three distinct initial cells 
(Graminem, Commelynaceae, Scitamineae, Liliaceae) ; (2) two distinct 
initials (Naiadaceae, Juncacem, Alismaeeae, Hydrocharideae). Among 
Dicotyledons, the existence of three initials is most frequent, occurring 
in two cases in Apetalae, ten in Dialypetalac Superiores, three in 
Dialypetalm Inferiores, and almost universally in Gamopetalas; while 
apical growth by two initial cells was observed in four cases among 
Apetalae, five among Dialypetalae Superiores, and in only one among 
Gamopetalae. 
Increase in Thickness of the Stem of Cucurbitaceae.f — Mr. M. C. 
Potter finds that the stem of the woody genera of Cucurbitaceae — 
Ceplialandra and Trichosanthes — increases in the normal way by a well- 
marked interfascicular cambium. In the herbaceous climbers belonging 
to the order with annual stems, the stem is strengthened by a ring of 
sclerenchymatous tissue situated in the cortical tissue between the 
epiderm and the vascular bundles. The woody perennial climbers, on 
the other hand, have no ring of sclerenchyme, and derive their support 
mainly from the xylem, which is constantly being renewed from a 
cambium ring. 
Morphological Origin of the Internal Liber.J — M. Lamounette has 
investigated this subject chiefly in connection with the hypocotvl 
(tigellum), cotyledons, terminal bud, and leaves. With regard to the 
root and hypocotyl he finds that those plants examined which have an 
internal liber (phloem) in their stem, may be divided into two classes, 
viz. those in which this structure occurs in the hypocotyl, and those in 
which it does not ; it never occurs in the root. The internal phloem of 
the hypocotyl is independent both of the phloem of the root and of the 
external phloem of the vascular bundles of the hypocotyl ; its formation 
is always later than that of the external phloem, and of the xylem- 
elements of the vascular bundles in conjunction with it ; it originates in 
the cells of the central medullary parenchyme. In the cotyledons the 
internal (upper) phloem is also always of later origin than the other 
elements of the vascular bundles, and originates in the procambial cells 
which have furnished these latter elements. Its period of formation and 
its origin are the same in the leaves. 
Since therefore the formation of an internal phloem is abnormal, and 
is due to a special evolution of certain parenchymatous cells, and is 
independent of the formation of the fibro-vascular bundle with which it 
is associated, the author considers that the term “ bicollateral,” usually 
* Ann. Sci. Nat. (Bot.), xi. (1890) pp. 283-350 (7 pis. and 5 figs.). 
t Proc. Cambridge Phil. Soc., vii. (1890) 5 pp. and 2 pis. 
X Ann. Sci. Nat. (Bot.), xi. (1890) pp. 193-282 (3 pis.). 
