1917] CURRENT LITERATURE 421 



4 cm. above the fluctuating surface of the water. These fluctuations of the 

 water level are great, as there are usually 3 floods each year, 2 in spring and 

 1 in autumn, the water at such times rising 1-6 m. The floating mat is made 

 up almost entirely of vertical rhizomes of the reed, which, with the aid of their 

 roots, retain much soil, the whole attaining a thickness of 0.8-2 m. The 

 aerial shoots vary in height from 1.2 m. to 5.15 m. This mat originates 

 attached to the soil, but becomes floating with the death of the basal rhizomes 

 and the action of such floods as are accompanied by only small depositions of 

 silt. The maximum size of units becoming detached is given as 2500 sq. m. 

 In the shallower water much of the reed mat remains permanently attached. 

 Little other vegetation is mingled with the Phragmitcs, its only competitor 

 being Typha angustifolia, which is apparently only able to inhibit its growth 

 for a short time. The reed seems to be succeeded by Cladium mariscus or by 

 an aggregation of species of Car ex. 



The most remarkable part of this paper is the hypothesis offered to explain 

 the difference in size of the reed, varying as it does from 1.2 m. to 5.15 m. 

 This Miss Pallis ascribes, not to any difference of variety, but to a difference 

 in age. She believes that the giant shoots, 5 m. in height, have arisen earliest 

 and at the base of the branch system of the rhizoids, and that with progressive 

 advancement toward the higher parts of the branch system the aerial shoots 

 have become gradually smaller and shorter. The change in size is thus a senile 

 degeneration which ultimately results in the death of the individual. Unfortu- 

 nately, the necessary experimentation to prove this theory would extend over 

 many years and hence could not be undertaken. Many of the facts appear 

 to support Miss Pallis' hypothesis, and most of her argument seems sound, 

 but some of the evidence seems to point to overcrowding being at least one 

 factor in the reduction in size of shoots. More data regarding the germination 

 and early growth of the reed should shed light upon the question of the dura- 

 tion of life of the Phragmites and its final senescence and death. — Geo. I). 

 Fuller. 



Taxonomic notes. — Ducke, 1 * in a presentation of new and little known 

 plants of the Amazon region, discusses 146 species, 102 of which are 



Legu 



cribed, 21 of which are Legu 



nosae. Among the new species there is a Zamia (Z. Lecointei). The paper 



appears m the initial number of a journal issued by the Botanical Garden or 

 Rio de Janeiro.. 



Greexman 1 * has published the second part of his monograph of Senecio, 

 including the Aurei (§ 6). He recognizes 48 species and describes 5 of them 

 as new. Of the new species, 2 are from the region of Newfoundland and 



13 Ducke, A., Plantes nouvelles on peu connues de la region amazonienne. Archiv. 

 Jard. Bot. Rio de Janeiro 1 : 1-159. pis. iq. 1915. 



x < Greenman, J. M., Monograph of the North and Central American species of 

 the genus Senecio. Part II. Ann. Mo. Bot. Gard. 3:85-194. *9 l6 - 



