ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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of the root or rhizel. The rhizel and radicle compose the root, while 
the tigel and gemmule constitute the stem. Four different methods of 
germination may be observed in Dicotyledons and Gymnosperms. The 
cotyledons may remain hypogeous, as in Monocotyledons ; or they may 
grow and expand in the air and the light. The growtli may take place 
in the tigel (as in Bicinus, Acer, Cucurbita, Tagetes, Convolvulus, &c.) ; 
or in the tigel and rhizel ( Euonymus , &c.) ; or only in the rhizel, which 
seems to take place most frequently, as in Ranunculacene, Cruciferae, 
Caryophyllacefe, Chenopodiacese, Umbelliferaj, Rubiace®, Coniform, &c. 
Origin of Polystely in Dicotyledons.* * * § — Dr. D. H. Scott points out 
that, while a polystelic structure of the stem is common in Vascular 
Cryptogams, occurring in the majority of ferns and in many species of 
Selaginella, in Phanerogams the monostelic structure is universal, except 
in two widely separated genera, Auricula and Gunnera. These two 
genera, however, resemble one another in having near relations which 
are aquatic in habit, and which have the reduced vascular structure cha- 
racteristic of aquatic plants. Dr. Scott suggests that these polystelic 
Dicotyledons owe their exceptional structure to descent from aquatic 
ancestors, and that it may be regarded as the anatomical expression of 
the return of plants of aquatic habit to a terrestrial mode of life. 
Endings of the Vessels in the Leaves, j — By macerating leaves for 
a long time in water, and then clearing with strong potash-lye, Herr P. 
Krutickij finds that the finest ends of the bundles are composed of two 
kinds of elements, tracheids, and long slender tubular cells, connected 
directly with the phloem of the stouter bundles, and not of tracheids 
only, as has generally been stated. The rows of these cells are in direct 
contact with the rows of tracheids only in one spot, which is near the 
end of the bundle; the remainder lie free in the parenchyme, near to 
the tracheid-buudle, and parallel to it. This observation is of con- 
siderable physiological importance in connection with the conduction of 
plastic substances from the leaves. 
Extra-phloem Sieve-tubes in the Root of Lythrum.J — Mdlle A. 
Fremont records the occurrence of extra-phloem sieve-tubes in the root 
of Lytlirum Salicaria. They have also been observed by Van Tieghem 
in several Monocotyledons, and among Dicotyledons in Cucurbita and 
Vinca, by Scott in Strychnos and Chironia, and by the author in 
Epilobium. 
(4) Structure of Organs. 
Variations in Floral Symmetry. § — Mr. W. Bateson and Miss A. 
Bateson record a series of observations on valuations in the floral sym- 
metry of certain plants with irregular corolla, the species observed being 
mainly Linaria spuria, Veronica Buxbaumii, hybrid Gladioli, and species 
of Streptocarpus. As a general result, the law is stated that variations 
which occur in such a manner as to produce a symmetrical result may 
* Ann. of Bot., v. (1891) pp. 514-7. 
t VIII. Congr. Russ. Naturf. u. Aertzc (Bot.), 1890, pp. GO-2. See Bot. Cen- 
tralbl., 1891, Beih., p. 417. 
J Journ. de Bot. (Morot), v, (1891) p. 448. Cf. this Journal, 1891, p. 618. 
§ Journ. Linn. Soc. (Bot.), xxviii. (1891) pp. 38G-424 (2 pis.). 
