ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
621 
parous,” i. e. the seeds germinate while still attached to the parent-tree. 
That the aerial roots in Pruguiera eriopetala and other species are 
organs of respiration, is unquestionable. In Bliizophora Mangle their 
chief function is a supporting one ; but they also possess large inter- 
cellular spaces which serve to assist respiration. Similar aerial roots or 
“ pneumatophores ” occur also in many other plants. All mangrove- 
trees contain large quantities of tannin, which is probably serviceable in 
preventing rotting. 
Stigmatic Disc of Vinca.* * * § — Sig. M. Pitzorno has studied the 
structure of the viscid discoidal expansion which lies beneath the tuft 
of hairs on the stigma of Vinca major , and which plays an important 
part in the process of pollination. He finds that the viscid substance 
which is exuded, during the time of flowering, from the periphery of 
the stigmatic disc, is a product of the secretion of special glandular 
hairs which clothe its margin. The exudation takes place by simple 
diffusion through the membrane of these hairs. The viscid substance 
appears to be the result of a chemical transformation of starch-grains 
which are present in abundance in the subjacent parenchyme ; the 
transformation takes place within the glandular hairs. 
Pollen of Strelitzia.f — Herr E. Palla describes the structure of the 
threads which are found among the pollen-grains of Streliizia reginse , 
and which have been mistaken by some writers for pollen-tubes. Each 
thread usually consists of two or three, less often of four cells, the length 
of which varies between 200 and 550 /a; the end of the thread is 
frequently closely attached to a pollen-grain. As to their origin, each 
thread was originally a row of cells belonging to the epidermal portion 
of one of the two pollen-sacs, which had become detached from the rest of 
the tissue shortly before the bursting of the anther. The threads appear 
to continue to grow in length among the pollen-grains after their sepa- 
ration. Their object appears to be to assist in the dissemination of the 
pollen, which is chiefly brought about by the agency of birds. 
Stomates in the Calyx. f — Herr W. Korella found that, out of 288 
species of plants examined, belonging to 192 genera and 58 families, 
stomates were entirely wanting in the calyx in only five species ; in by 
far the greater number they were present on both surfaces. Their size 
and their distribution over the surface of the sepals vary greatly. 
Fruit and Seed of the Juglandeae.§ — Sir John Lubbock describes 
the structure and development of the fruit and seed of Pterocarya, and 
compares them with those of the walnut. The fruit of the former is 
winged, while that of the latter is not. While the cotyledons of Ptero- 
carya are leaf-like and aerial in germination, those of the walnut never 
emerge from the seed, but are curiously folded by the efforts made to 
occupy the interior of the nut. The seeds of the walnut are large and 
contain a supply of nutriment, which causes them to be dispersed by 
* Nuov. Giorn. Bot. Ital., xxxviii. (1891) pp. 280-2. 
f Ber. Deutsch. Bot. Gesell., ix. (1891) pp. 85-91 (1 pi.). 
X ‘ Ueb. d. Yorkommen u. d. Vertkeilungd. Spaltoffnungen auf d. Kelchbl attorn,* 
Kbnigsberg, 1889, 68 pp. and 1 pi. See Bot. Centralbl., xlvi. (1891) p. 385. 
§ Journ, Linn. Soc. (Bot.), xxviii. (1891) pp. 217-54 (6 figs.). 
