1 894. NOTES AND COMMENTS. 333 



Recent Researches in Botany. 



One of the early numbers of Natural Science contained an 

 account of Treub's researches into the embryology of the genus 

 Casuarina. So many new and important facts were brought to light 

 in the course of his work that Treub was impelled to separate the 

 family Casuarineae, which this single genus constitutes, from the 

 apetalous group of Dicotyledons, where it had hitherto been placed 

 near the Cupuliferae, and make it the sole member of a new class of 

 flowering plants. This new class he named Chalazogams, the rest of 

 the Phanerogams forming one great class of Povogams, the main 

 distinctive character being the mode of approach of the pollen-tube to 

 the embryo-sac in the process of fertilisation. In the second class the 

 tube followed the normal course, namely, down the micropyle of the 

 ovule, and so directly on to the top of the embryo-sac ; but in the 

 Casuarineae an indirect route was taken, the tube passing along the 

 side of the ovule down the chalaza, and entering one of the many 

 macrospores or embryo-sacs at the lower end. Other points of interest 

 in the embryology of this anomalous genus were the existence, not of a 

 single macrospore,but of a number, which formed a sporogenous tissue, 

 and of which several might develop very considerably ; the presence of 

 long tails to the developing macrospores, up which the pollen-tube 

 ultimately made its way ; the frequent appearance in the sporogenous 

 tissue of pitted cells (tracheids), for which Treub could suggest no 

 function ; the branching of the pollen-tube, with the formation of 

 recurved blind endings ; the absence of antipodal cells in the 

 embryo-sac ; and finally the early assumption of a cell-wall by the 

 egg-cell before the arrival of the end of the pollen-tube in its 

 neighbourhood. 



In the Transactions of the Linnean Society (2nd series. Botany, 

 vol. iii., p, 409), Miss Benson now describes the results of some work 

 on the Embryology of the Amentiferae which, following on the above, 

 are of great interest and importance. In the first place, she shows 

 that it is no longer possible to classify merely the Casuarineae by 

 themselves as Chalazogams, for in the alder, birch, hazel, and hornbeam 

 the pollen-tube takes the same indirect route, while there are other 

 points of agreement between the strange Australian genus and our 

 British catkin-bearing trees. Thus, whereas in the normal type 

 hitherto found to be almost universal among Angiosperms, the 

 macrospore originates from one of a single "axilerow" of cells 

 (archesporium), in the genera studied by Miss Benson a large 

 number of such rows was present, forming a sporogenous tissue, in 

 which, moreover, spindle-shaped cells frequently arose, developing, in 

 the case of Castanea, into large and conspicuous tracheids. The 

 prevalence of "caeca," formed by the embryo-sac, recalling the 

 " tails " of the macrospores in Casuarina, is remarkable, as is also the 

 branching of the pollen-tube and the formation of recurved endings. 



