ZOOLOGY AND BOTANY, MICliOSCOPY, ETC. 467 



differ from " thylloses " in that the whole of the free part of the wall 

 grows out, while in true " thylloses " only the outer membrane grows 

 out. The author does not agree with Mellink in regarding these out- 

 growths as traumatic thylloses, but regards them as special callus-forma- 

 tions which the plant makes for its own protection. 



Reproductive. 



Morphology of Juniper.*— G. E. Nichols has studied the American 

 Juniper communis var. depressa, with the following results. The author 

 finds that the staminate cones originate in the summer preceding pollina- 

 tion. The archesporium arises from the hypodermis at the base of the 

 sporophyll, and its outermost cells give rise to the tapetum and inner 

 sporangium-wall : the outer sporangium-wall is derived from epidermal 

 cells. At the completion of the heterotypic division of the microspore 

 mother-cells two resting daughter-nuclei are formed, but no wall ever 

 separates them. The mother-cell eventually forms four cavities within 

 which the microspores are formed. About a year elapses between polli- 

 nation and fertilisation. The pollen-tube quickly penetrates the nucellus, 

 often branching, and the primary nucleus divides to form a tube-nucleus 

 and generative-cell-nucleus ; the latter divides subsequently to form 

 stalk-nucleus and body-cell-nucleus. No true stalk-cell is ever formed. 

 Three or four male cells may be produced from one body-cell, but only 

 two are functional. The female archesporium arises in the lower part 

 of the nucellus, but it cannot be recognised at the time of pollination. 

 Only one archesporial cell becomes a true mother-cell, while non-func- 

 tional cells give rise to the tapetum. Usually only one nucleus resulting 

 from heterotypic division undergoes homotypic division. There is a 

 two-layered megaspore membrane, and the tapetum persists until pro- 

 thallial tissue is formed. Four to ten archegonia are formed, all enclosed 

 in a single layer of jacket-cells. Division of the central cell nucleus is 

 simultaneous in all the archegonia of a group. No ventral cell is ever 

 formed. The mature egg-nucleus contains both nucleoli and pseudo- 

 nucleoli. Male and female nuclei fuse during the resting stage, and the 

 fusion nucleus is surrounded by starch derived from the male cell. 

 Usually eight free nuclei are formed before walls appear. The upper 

 cells give rise to suspensors and rosette-cells. 



Physiology. 



Nutrition and Growth. 



Transpiration.f — 0. Renner has made numerous experiments dealing 

 with the transpiration of plants under different conditions. The plants 

 used included Nuptor, Hydrangea, Aconitum, Gentiana, Tradescantia, 

 etc., and experiments were made with varying intensities of light, in 

 motionless atmosphere and during windy weather. The chief results are 

 as follows :- — Transpiration is to be regarded as a static diffusion, and is 

 dependent upon and proportional to the difference in aqueous tension of 

 the cells and of the atmosphere. Since this tension is itself dependent 



* Beih. Bot. Centralbl., xxv. (1910) pp. 201-41 (10 pis. and 4 figs.), 

 f Flora, c. (1910) pp. 451-548 (25 figs.). 



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