54 SUMMARY OF CURRENT RESEARCHES RELATING TO 



definite egg-apparatus and antipodals, and especially the increase in the 

 number of nuclei. There is a striking similarity between the structure 

 of the embryo-sac in Peperomia and in Gnetum among Gymnosperms. 

 The typical embryo-sac may have been derived from one like Peperomia 

 by the suppression of a nuclear division. The marked polarity, and the 

 specialisation of the egg-apparatus and antipodal cells, are probably 

 secondary characters, and the fusion of the polar nuclei finds its proto- 

 type in the multiple fusion of the nuclei in Peperomia to form the 

 endosperm-nucleus. The egg-cell probably represents an archegonium 

 reduced to a single cell, and the synergidse may also represent potential 

 archegonia, although they may with equal probability have been derived 

 from vegetative prothallial cells. The remaining structures — the polar 

 nuclei (and the result of their fusion, the endosperm-nucleus) and the 

 antipodal cells represent vegetative prothallial tissue. The fusion of the 

 polar nuclei is in no way to be regarded as a sexual process ; the regular 

 occurrence of a multiple fusion in Peperomia is a strong argument 

 against such an assumption. It is probably to be interpreted as a 

 stimulus to further growth. The fusion of the second pollen-nucleus 

 with the endosperm-nucleus must be considered as more or less acci- 

 dental. 



Physiology. 

 Nutrition and Growth. 



Physical Conditions of Tuberisation in Plants.* — Noel Bernard 

 discusses the bearing of results recently obtained by M. Laurent on his 

 own theory that the development of buds into tubercles is a symptom of 

 a general modification of the internal constitution of a plant by the 

 action of endophytic fungi which inhabit its organs of absorption. 

 M. Bernard repeats the experiments of M. Laurent, and confirms the 

 results arrived at by that author. Shoots of potatoes cut off and plunged 

 into a solution of saccharose, glycose, glycerin, and other solutions of 

 sufficient concentration, develop tubercles from the buds on their aerial 

 stems. He concludes that the result is clue, not to the specific properties 

 of the dissolved substance, but to the degree of concentration of the 

 solution. In every case there is a critical concentration of the solution 

 below which the buds develop into leafy branches, while if it be ex- 

 ceeded tubercles are formed. It would appear that the tuberisation of 

 the buds depends directly on the realisation of a certain degree of con- 

 centration of the sap which nourishes them in dissolved substances. 

 The presence in the tissues of the plant of parasites capable of effecting 

 by their diastatic secretions an increase in the complexity of the 

 molecular compounds is one of the conditions which may lead to this 

 state. Other factors, especially those which govern transpiration, may 

 have the same effect. Hence M. Laurent's results are not inimical to 

 the author's parasite theory of tuberisation. 



Photosynthesis.! — E. Griffin has investigated the relative amount 

 of photosynthetic action in green leaves when the upper and under 

 surfaces respectively are illuminated. He wished to test the hypothesis 



* Comptes Keiidus, cxxxv. (1902) pp. 706-8. t Tom. cit., pp. 303-5. 





