364 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
as in Botrychium , Helminthostachys, and many species of Equisetum , the 
peridesms also coalesce ; and when the fusion of the vascular bundles 
is complete, as in the two former genera, the general external peridesm 
simulates a pericycle, and gives the appearance of a monostelic stem. 
In Marsilea, many ferns, and some species of Auricula , we have a gamo- 
polystelic structure in which the pericycles are united into a general 
external and a general internal pericycle ; a structure very liable to be 
confounded with the general external and general internal peridesm in 
the gamo-astelic structure. 
Abnormal Formation of Secondary Tissues.* — Herr H. de Vries 
describes the mode of formation of secondary tissues in the following 
abnormal cases, viz. : — a flower-stalk three years old of Pelargonium 
zonale ; formation of wood in potatoes ; in turnips two years old ; ab- 
normal formation of wood under the influence of galls ; excrescences in 
leaves. As a general rule, conducting organs like flower-stems and leaf- 
stalks only last so long as the organ which they have to bear ; when, 
from any exceptional cause, the life of the latter is prolonged beyond its 
normal limits, then the formation of secondary tissue is incited in the 
part that bears it. 
Sieve-septum of Vessels. f — Herr 0. Eodham describes the occur- 
rence of peculiar vessels in Tecoma which are traversed transversely by 
a septum perforated in a sieve-like manner. They are found both in 
the outer normal woody structure and in the inner wood formed out of 
the secondary meristem in the pith, several being sometimes seen in 
the same transverse section. 
Order of Appearance of the Vessels in the Flowers of Tragopogon 
and Scorzonera.J — M. A. Trecul states that if one follows the order of 
appearance of the vessels in the interior of the bracts of the involucre 
of Tragopogon pratensis, porrifolius , &c., one finds that the first vessel of 
the median vein commences free at the two ends in the middle region 
of the bract, or sometimes even higher. In the flower itself the vessels 
of the stigmatic branches are formed after those of the corolla, but 
before those of the style. It is only after the appearance of vessels in 
the parts of the flower already mentioned, that the parietal vessels of 
the inferior ovary are formed. These usually result from the basal 
prolongation of five bundles or original substaminal groups. 
Independence of Fibro-vascular bundles in the appendicular organs.§ 
— M. D. Clos applies the term exoneurosis to the separation of the veins 
in the appendicular organs of plants, and their emergence in the form of 
teeth, spines, or bristles. A good illustration of exoneurosis is furnished 
by the transformation of leaves into spines in the barberry, and various 
other examples are described, especially in the case of stipules. In 
addition to stipules, this phenomenon is most frequently displayed in 
submerged organs, in the organs in the immediate vicinity of the flower 
or of the inflorescence, and in the parts of the flower itself, especially in 
the sepals. 
* Jahrb. f. Wiss. Bot. (Pringsheim), xxii. (1890) pp. 35-72 (2 pis.). 
f Ber. Deutsch. Bot. Gesell., viii. (1890) pp. 188-90 (2 figs.). 
X Comptes Rendus, cxi. (1890) pp. 327-33. 
§ Mom. Acad. Sci. Toulouse, ii. (1890) pp. 218-67 (1 pi.). 
