ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
199 
appear to be confined to a single species of Olyra, and Dr. Muller is 
unable to assign to them any function in the life of the plant. 
Anatomy and Histogeny of Strychnos.^ — Dr. D. H. Scott and Mr. G. 
Brebner have endeavoured to clear up, as regards the anomalous genus 
Strychnos, some of the points which previous investigations have left 
obscure. The general structure of the stem, its development, and the 
development and structure of the phloem-islands, are all carefully 
described, and also the structure of the root. The authors recapitulate 
the results of their investigations as follows: — (1) The external phloem, 
though but little developed, contains sieve-tubes and companion-cells of 
normal structure, with the exception that nuclei are found in the mature 
sieve- tubes. The latter fact is perhaps an indication of their rudi- 
mentary character. (2) («) The medullary phloem-groups, as shown 
by their development and by their course, form an integral part of the 
leaf-trace-bundles, which are therefore from the first of bicollateral 
structure, (h) These medullary groups grow by means of a special 
cambium lying on the outer side of each group. (3) (a) The phloem- 
islands, or interxylary phloem-strands, are formed centripetally by 
certain portions of the normal cambium, (b) The phloem-islands con- 
tinue to grow after they are inclosed in the wood, by means of the 
cambium layer on their inner side. (4) The roots, in so far as they 
have a pith, possess medullary phloem-groups similar to, but smaller 
than, those of the stem, and increasing, like the latter, by means of a 
centrifugally active local cambium. The authors then conclude with 
various comparative considerations. 
Floating-tissue of Nesaea verticillata.f — Mr. J. Schrenk states that 
Nessea verticillata grows in stout clumps along the swampy borders of 
pools and lakes. In the months of July and August many of the slender 
wand-like stems sent up by the root-stock have attained considerable 
length, and begin to bend downward by their weight until the apex of 
the stem touches the surface of the water, when they curve up again. 
At the region of contact between stem and water a swelling will be 
noticed about 10 mm. below the apex. The apex continues to grow 
more or less rapidly, while the swelling below it increases, and extends 
over a distance of 20-40 cm. The epiderm of the stem at this region 
shows longitudinal fissures ; and underneath a snow-white, soft, elastic, 
spongy tissue is seen, the function of which is to prevent the apex of 
the stem from sinking below the surface of the water and to keep the 
stem afloat. It consists of parenchymatous cells of peculiar shape and 
arrangement. The walls of these cells are very thin, and consist of 
cellulose ; they contain a delicate lining of protoplasm, in which slow 
but distinct currents may be noticed, and also small rounded starch-grains. 
The development of the floating-tissue is as interesting as its func- 
tion, the meristem producing it being first noticed at the sides and upper 
part of the horizontal floating stem ; and consequently at a later stage 
the aerenchyme J is more copiously developed at those places than on 
the lower side where the roots grow. 
* Ann. of Bot., iii. (1889) pp. 275-302 (2 pis.). 
t Bull. Torrey Bot. Club, xvi. (1889) pp. 315-23 (3 pis.). Cf. this Journal, 1889, 
p. 779. X Cf. swpra, p. 197. 
