432 SUMMARY OF CURRENT RESEARCHES RELATING TO 



In A. alpina the male plant is exceedingly scarce. In the develop- 

 ment of the embryo-sac there is no tetrad-formation ; the mother-cell 

 gives birth to the embryo-sac without division ; the oosphere develops into 

 the embryo parthenogenetically, and the endosperm arises from the two 

 polar nuclei without any fusion. The cycle of development of the plant 

 is completed without either increase or reduction in the number of 

 chromosomes. 



The paper concludes with some theoretical considerations respecting 

 the relationship to one another of the various modes in which the embryo 

 is produced in spermatophytes. 



Parthenogenesis and Chalazogamy in Alchemilla. * — In all the 

 sj.ecies examined of this genus belonging the section Eualchemilla, 

 Sv. Murbeck y states that true parthenogenesis is more or less constant. 

 In A. alpina the ovum-cell begins to divide in the unopened flower-burl, 

 the anthers being still closed and destitute of pollen. The mature 

 ovule has the appearance of a naked nucellus, owing to the coalescence 

 with it of the single integument at the micropyle. In the young 

 nucellus, when the integument first begins to be formed, there is a 

 hypodermal group of archesporial cells. Each cf these archesporial 

 cells breaks up by transverse septation into a covering cell and an 

 embryo-sac mother-cell; from any of these latter an embryo-sac may be 

 formed. One or more (usually from two to six) of these embryo-sacs 

 penetrate through the epidermal cap composed of the covering cells, as 

 far as the tissue of the integument. The divisions of the nucleus which 

 lead to the formation of the two polar groups take place quite normally. 

 The oosphere, synergids, and antipodals, have the normal position and 

 structure ; from the former the embryo is formed without any process of 

 impregnation ; there is nothing unusual in its later development. The 

 fusion of the polar nuclei frequently takes place at a late period ; the 

 central nucleus thus formed divides immediately, and produces two 

 endosperm-nuclei. In the development of the embryo-sac, in fact during 

 the whole of the life of the plant, the number of chromosomes appears 

 to remain unchanged. 



In Alchemilla arvensis,] belonging to the section Aphanes, the process 

 of parthenogenesis is replaced by one of chalazogamy. As in other 

 species of Alcliemilla, the micropyle of the single integument is closed 

 at an early period. The pollen-tube descends through the style, and 

 works its way through the short funicle to the base of the nearly ortho- 

 tropous ovule; it then ascends within the integument until it reaches 

 the level of the germinal vesicles. The actual act of impregnation 

 of the oosphere was not observed, but the process appears to take place 

 in the normal way. 



Development of the Endosperm and Testa of Corydalis. j. — In 

 Gorydalis cava, according to G. Tischler, the resting nuclei of the 

 parietal layer of the embryo-sac exhibit a peculiar arrangement of the 



* Lund's Univ. Arsskr., Bd. xxxvi. No. 7 (1901) 46 pp. and 6 pie. See Bot. Ztg., 

 ]ix. (1901) 2 ,e Abt., p. 129. 



t Tom. cit., No. 9, 20 pp. and 2 pis. See Bot. Ztg., lix. (1901) 2"> Abt.. p. 135. 



{ Verhandl. naturbist.-ined. Ver. Heidelberg, vi. (1900) pp. 351-80 (2 pis.). See 

 Bot. Centralbl., lxxxv. (1901) p. 365. 



