ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 199 



structures, the theory of the author is that they are adventitious organs, 

 the formation of which uses up the food-material that would otherwise 

 be employed in the production of pollen and ovules. 



Formation of the Pollen in the Asclepiadese.* — Prof. E. Straslmrger 

 has followed the formation of the pollen in Asclepias Cornuti, and Las 

 found it to be much more closely in accordance with that in typical 

 Angiosperms than has hitherto been supposed. He does not confirm the 

 statement of Vines that in Asclepias ettch pollen-niother-cell develops 

 directly into a pollen-grain without division. He states, on the other 

 hand, that the pollen-grains of which the pollinium is composed are 

 formed in fours in the mother-cells, corresponding to the divisions in 

 the embryo-sac mother-cells ; but they present the peculiarity that the 

 two divisions take place in the same direction, so that the four daughter- 

 cells form a row instead of an ordinary tetrad. In the nucleus of the 

 pollen-mother-cells he found the ordinary number of chromosomes to 

 be ten, a number not yet recorded in the reduction phenomena of gene- 

 rative cells. The chromosomes are very small, notwithstanding the 

 comparatively large size of the resting nucleus. With regard to the 

 presence of centrosomes in the division of the pollen-mother-cells, 

 Strasburgcr's results were entirely negative ; he was unable to confirm 

 the statements made by other observers of their presence in similar con- 

 ditions in other Angiosperms, and by Raciborski in Asclepias. Similar 

 results were obtained with Cynanchum Vincetoxicum. 



An examination by T. C. Fryef of several species of Asclepias and 

 Acerates led to results similar to those obtained by Strasburger. A care- 

 ful study showed that in the species examined the development of the 

 microsporanges is the same in general as in other plants [Angiosperms] ; 

 while there are no indications of the phylogenetic history of the reduc- 

 tion in number. The primary sporogenous cells become the pollen- 

 mother-cells without further division. The latter divide each into four 

 with the usual phenomena of tetrad-division. 



Abnormal Flowers of Forsythia viridissima Lindl.J — M.Velenovsky 

 describes abnormal flowers in which the sepals have become leaf-like, 

 while the corolla is not only reduced in size, but also in number of 

 parts. Some flowers showed only two free petals, which alternated with 

 the inner sepals and stamens, making a regularly dimerous flower. In 

 others the two petals were more or less split lengthwise, showing, there- 

 fore, various transition stages to the normal whorl of four, character- 

 istic both of the genus and family to which it belongs. These cases 

 support Eichler's view of the origin of the typical tetramerous corolla of 

 Oleaceae from doubling of two petals, aud may be compared, from this 

 point of view, with Fraxinus dipetala. 



Physiology. 

 Reproduction and Embryology. 



Double Fertilisation in the Solanaceae and Gentianaceae. § — In 

 addition to the Composite, the only order of GaniopetalsB in which the 



* Eer. Deufcch. Bot. Ges., xix. (1901) pp. 450-61 (1 pi.). 



t Bot. Gnzette, xxxii. (1901) pp. 325-31 (1 pi.). 



I Oeaterr. Bot. Zeitschr., li. (1901) pp. 325-8. 



§ Comptes Rendus, cxxxiii. (1901) pp. 1268-72. Cf. this Journal, 1901, p. 173. 



