ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 451 



the cells are well differentiated arid form a roundish cell-complex, the 

 chief function of which is the conversion of the material stored in the 

 embryo-sac. It is represented by the Graminege, Aracea?, Ranunculaceie, 

 Mimoseae, Caasalpiniese, and occurs also, in combination with the third 

 type, in the Liliacese, Iridacese, Zingiberacese, Boraginaceaj, and 

 Solanaceaj. In the third type the cells form individually or together an 

 elongated structure serving as haustoria for the embryo-sac ; this 

 type is exemplified mainly in Rubiacese and Compositse. 



Apogamy in Alchemilla.* — E. Strasburger comes to the following 

 conclusions as the result of the study of this phenomenon in several 

 species of the section Eu- Alchemilla. Thirty-two bivalent chromosomes 

 are present at the reduction division of the pollen-mother-cells. In the 

 ovule of apogamous species one or several archesporial cells appear as 

 embryo-sac mother -cells. Their nuclei pass through the prophase 

 stage of the reduction division as far as the synapsis stage. At this 

 point the embryo-sac mother-cell becomes vegetative, its nucleus passing 

 over from the synapsis into the typical method of division. The pro- 

 ducts of division of the thus altered archesporium cell are due to a 

 vegetative, not to a generative process. They must be regarded not as 

 the beginning of a new generation, as macrospores, but as tissue cells of 

 the parent ; and the resulting development is apogamous. The embryo- 

 sacs which are formed from this tissue contain an apogamous egg-cell,, 

 the nucleus of which has a vegetative number of chromosomes, and the 

 embryo is an apogamous development of this egg-cell. 



Some of the subnival species have normal pollen, and these also 

 develop in their ovules, by the process of reduction division, macrospores 

 from embryo-sac mother-cells. The embryo-sac which develops from 

 the macrospore contains a generative egg with a reduced number of 

 chromosomes in the nucleus, and produces an embryo only as the result 

 of fertilisation. The author also finds that the normal sexual species 

 are chalazogamic, and that some of them hybridise. He suggests that 

 excessive mutation has caused the weakening of the sexual power in the 

 Eu-Alchemilleae, and with failure of fertilisation apogamous reproduction 

 has been adopted. The genera Rubus and Rosa, in spite of their strong 

 polymorphism, have hitherto remained sexual ; the author finds that 

 the macrospore develops from the embryo-sac mother-cell by a process of 

 reduction division, and the egg is a generative one. It is also pointed 

 out that dicecism has in many cases formed the stimulus to the assump- 

 tion of apogamy, the separation of male and female individuals tending 

 to a suppression of fertilisation. 



Notes on the Fruits of Opuntia.f — J. W. Tourney has studied 

 various species of this genus, which is evidently of comparatively recent 

 origin and development. Owing to the instability of the characters 

 available for the systematist, no one has been able to make a satisfactory 

 taxonomic arrangement of the species, nearly one hundred of which 

 (including varieties) have been described from the arid regions of the 

 south-western United States and north-western Mexico. The shoot is 



* Jahrb. wiss. Botan., xli. (1904) pp. 88-164 (4 pis.). 



t Bull. Torrey Bot. Club, xxxii. (1905) pp. 235-9 (2 ph.). 



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