558 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tions, but any condition which tends to decrease osmotic pressure, may 

 cause male plants to produce female organs ; conversely, but far more 

 rarely, increase of osmotic pressure will bring about the formation of 

 female organs. 



There is no proof that seeds are ever formed in H. Lupulus in the 

 absence of fertiHzation, for in spite of the absence of a micropyle, the 

 pollen-tube can penetrate the ovular tissues as far as the embryo-sac. 

 It is possible, however, for seeds to form under the influence of foreign 

 pollen, such as that as of H. japonicus and of the Hemp, but such seeds 

 have only abnormal and abortive embryos. In the former case true 

 fertilization occurs, but in the latter case development is the result of 

 simple contact between the pollen-tube and the oosphere, there being no 

 true fusion. Fertilization is not necessary for the development of the 

 fruit of H. Lupulus, but it causes greater activity in growth. In con- 

 clusion, the author points out that these experiments with Humulus show 

 that it is possible to modify the sex of dioecious plants, but that changes 

 of sex thus produced are limited to a small proportion of individuals, 

 while in the greater number the changes are neither complete nor 

 definite. Also, that it is possible to bring about abortive developments 

 of the female gametes of plants comparable to those obtained in such 

 animals as sea-urchins, and it is probable in both cases that arrested growth 

 is due either todeficiency of male chromatic substance or to an excessively 

 heterogeneous chromatic association. 



Projection of Seeds of Oxalis.* — V. Royale has studied the mechan- 

 ism by means of which the seeds of Oxalis are projected from the fruit. 

 The author finds two reasons for disagreeing with those writers who 

 maintain that projection is due to the structure of the outer integument 

 of the seed. In the first place, the structure of this integument is 

 identical with that of the seed of Biopltytum, where no such projection 

 occurs ; secondly, in almost every instance the seed retains its integu- 

 ment after projection. The present investigations prove that the seed 

 is first detached from the fruit by the breaking down of the suberized 

 tissue at the point of attachment of the seed to the fruit-wall. The 

 seed then becomes enveloped in a thick layer of mucilage, which, by 

 its turgescence, projects the seed through the suture of the carpels. 

 Thus the external integument plays no part in the projection which 

 depends directly upon the periseminal mucilage and indirectly upon the 

 structure of the carpels. 



Physiology. 

 Nutrition and Growth. 



Influence of Water on Roots of Trees.*— G. Boudois has studied 

 the modifications in the morphology and anatomy of roots of trees 

 growing by the water-side, where the roots are actually growing in 

 water. The author finds that under these conditions the rapidity and 

 extent of growth of the primary roots is greatly increased, while the 



* Ann. Sci. Nat., xviii. (1913) pp. 25-33 (8 figs.). 

 t Ann. Sci. Nat., xviii. (1913) pp. 1-24 (9 figs.). 



