664 SUMMARY OF CURRENT RESEARCHES RELATING TO 



regarded as secreting an enzyme and absorbing the food derived by 

 digestion of the reserve food-substances in the integument. 



During growth of the embryo-sac mother-cell a large number of 

 coarse fibres occur in the cytoplasm, and persist through diakinesis of 

 the first division. The spindle in both pollen and embryo-sac mother- 

 cell is of multipolar origin, and there is no trace of centrosomes. A 

 reduced number of chromosomes appears in the prophase of the first 

 division of the pollen and embryo-sac mother-cells, ten in Crucianella, 

 twelve in Asperula. These numbers are maintained throughout subse- 

 quent divisions. From the mode of division the author concludes that 

 they are true tetrad divisions, and the four resultant cells are spores. 

 The author also refers to the question — at what point in the life cycle 

 does the gametophyte start ? The two periods of development have 

 been merged into one another to different degrees in different plants. 

 In extreme cases, as Lilium, the gametophyte appears to begin histo- 

 logically with the embryo-sac mother-cell, and where four spores are 

 produced it may be regarded as an individual by coalescence, having its 

 origin in four like vegetative cells whose primitive function has been 

 lost. As Juel and Murbeck have shown in Antennaria and Alchemilla, 

 true tetrad mitoses do not occur in parthenogenetically reproduced 

 plants. 



In view of the fact that the course of the pollen-tube may be inter- 

 cellular, or pass through the ovary cavity in related species, the author 

 infers that its behaviour is of no practical significance) from the point of 

 view of phylogeny. Chemotropism is assumed to be the important 

 factor in guiding the pollen-tube, and the suggestion is made that the 

 synergidae are the source of the stimulant. 



Development of Ovule and Seed in Rosaceae.* — F. Pechoutre has 

 studied the development of ovule and seed in a large number of species 

 representing the different tribes of the order. He finds, contrary to the 

 assertions of Baillon, who considers the ovules of most indigenous 

 Rosacea? to be monochlamydeous, that almost all are dichlamydeous ; 

 Geum, Fragaria, Potentilla, and Alchemilla alone of the genera studied 

 having only an external integument, the internal being absorbed. The 

 development of the integuments shows great homogeneity throughout 

 the order. The internal originates from four epidermal cells, which 

 generally arise by tangential division of a single epidermal cell, or 

 sometimes of two neighbouring cells. They appear at the level of the 

 base of the nucellar projection, after the differentiation of the embryo-sac 

 mother-cells. The external tegument originates from a subepidermal 

 cell behind and close to the dividing epidermal cell. Later on cell- 

 division extends to neighbouring subepidermal cells and the covering 

 epidermal cells. The external tegument generally appears after the 

 internal. Hence the development of the ovular teguments in Rosacea? 

 conforms to the rule general to all Dialypetalse. Even in the most 

 pronounced cases of concrescence there is never any confusion of the 

 initials. The variations which appear depend solely on the relative 

 position of the respective initials. In Pirese, where a distance of about 

 two epidermal cells separates the initials, the teguments arise as two 



* Ann. Sci. Nat., xvi. (1902) pp. 1-158 (166 figs.). 



