loop) CURRENT LITERATURE 167 



Mucilage ducts in Pipereae.— In considering the genera of the Piperaceae, 

 two tribes are recognized by Van Tieghem, 1 * namely Pipereae and Peperomieae ; 

 while the Saururaceae are kept as a distinct family, as suggested a hundred years 

 ago by L. Cl. Richard. By Casimir DeCandolle the Saururaceae were replaced 

 in Piperaceae as a tribe; and then separated by Engler. In speaking of Piper- 



TlEGHEM 



From an 



anatomical point of view the Piperaceae have long attracted much attention, 

 especially on account of peculiarities in stem structure, which at the same time are 

 characteristic of the respective tribes. For instance, in the Pipereae the stem 

 exhibits a normal monostelic structure, with the broad stele surrounded by a 

 well-differentiated endodermis, and possesses at least two concentric bands of 

 mestome bundles. In the Peperomieae, on the other hand, the stem structure 



chizostelic 



endodermis. Common to 



both tnbes, however, is the presence of roundish oil cells with the cell wall sub- 



times 



eaf. In certain Pipereae still another secreting system occurs, which is now 

 °r the first time described. It consists of a single duct or several broad ducts 



ducts 

 cells. 



length 



are lysigenous, since they arise from the destruction of a row of secreting 

 ^ hey occur in the pith of the stem, mostly a very broad one in the center 



^ several narrower ones in a band around this and alternating with the inner- 



mestome strands. They contain a colorless mucilage, and are surrounded 

 ^ ; Sma celIs > not ably smaller than those of the surrounding pith parenchyma. 

 thiT *TT ° f Secretory ducts belonging to the stem stele is readily followed 

 the^d internodes > but disappears completely in the nodes. In the leaf 

 hadro UCte ,° CCUr in the P etiol e, in the parenchyma located on the ventral (the 

 k tra^- ^ ° f the ar ° h formed b X the ™estome strands; thence they may 

 fte auth m the . midrib of the leaf blade, from the base to apex. Although 

 detert\°V Xamined various representatives of the Peperomieae, he failed to 



in?. 

 stack 



Among 



macro 



Dii»r xt species of Heckeria; while they are not developed in Macro- 



PP*. ^ematanthera, and Zippdia.-THEO. Holm. 



WhutionT m aquatic P la nts.— Francois 18 has offered a very interesting con- 

 nal as w \\ ** knowIed g e of aquatic plants with notes on their structure, exter- 



/ ^ lnternal) ^ on th eir seedlings, the text containing many well- 

 ^ Ures - Special attention is given to the vegetative reproduction of such 



17 Van T 



Bot. iv „' IEgh em, Ph., Sur les canaux a mucilage des Piperees. Ann. Sci. Nat. 

 Al 7-n 7 . I9o8< 



IX-7:2 5- x 9 q& S ' L *' Recherches sur les Pontes aquatiques. Ann. Sci. Nat. Bot. 



