512 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Perisperin is at present known in the seeds of Piperales, Aristolo- 

 chiales, Polygonales, Centrospermse, and Ranales among the Dicotyledons. 

 All of these orders are, as pointed out by Schimper and Lesqnereux, old 

 geologically, and may represent branches of a single stock or phylum of 

 the Dicotyledons. The Piperales are probably |inuch more closely related 

 to Polygonales than would appear from the position assigned to them by 

 Engler. 



A study of the germination in Peperomia and HecTceria indicates 

 that the aleurone-containing endosperm of these forms acts as a digesting 

 and absorbing apparatus for transferring the starch stored in the 

 perisperm to the embryo. In several genera of the Cannacege, Poly- 

 gonaceas, Phytolaccacere, Caryophyllaceaa, and others, a thin layer of 

 endosperm separates perisperm and embryo and seems to serve the same 

 function as in Peperomia and HecTceria. The embryo sporophyte is 

 perhaps everywhere nourished through the gametophyte and not 

 directly by the parent sporophyte. 



Morphological Study of Asclepiadacese.* — T. C. Frye has studied the 

 floral development and embryogeny in several species of Asclepias. He 

 finds that the umbels are terminal and that the parts of the flower 

 appear in centripetal succession, the members of each set arising 

 simultaneously, and there is no confluence of primordia. The stamens 

 and petals arise early from a common ring slightly elevated above the 

 insertion of the other sets ; the tube of the corolla seems to be of toral 

 origin. The stamens are remarkable in the development of intercellular 

 spaces ; the horn and head are lateral outgrowths from the filament and 

 composed largely of extremely loose tissue ; the horn contains no 

 vascular tissue. The top of the " head " formed by fusion of the tips of 

 the carpels, and not the functional stigma, is believed to be homologous 

 with the stigma of normal angiosperms. In general, Corry's account 

 of the formation of the caudicles and corpuscula is corroborated. 



The generative cell divides in the normal way near the tube-nucleus ; 

 the division occurs before the formation of pollen-tubes. The pollen- 

 tubes from the same pollinium all enter the same ovary ; the tube-nucleus 

 gets no further than the upper part of the ovary. 



The ovule has one integument, and the nucellus is a single row of 

 cells enclosing the sporogenous row. A single hypodermal archesporial 

 cell forms a row of four megaspores without the formation of a parietal 

 cell. Occasionally there is more than one archesporial cell ; in the 

 formation of the megaspores the daughter-cells do not divide simul- 

 taneously. The female gametophyte develops normally. Double 

 fertilisation was observed in Asclepias Cornitti, one of the male cells 

 fusing with the antipodal polar nucleus ; fertilisation may occur before 

 or after the fusion of the polars. A few tracheids were found in the 

 ovules near the antipodal cells. 



The oospore rests until the endosperm has become 16-celled or more. 

 The pappus is composed of single-celled uninucleate trichomes ; the 

 double wall of the pod originates in the rupture of the parenchymatous 

 tissue within the wall of the carpel. 



* Bot. Gazette, xxxiv. (1902) pp. 389-413 (3 pis.). 



