ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 669 



however, do not diminish, and are found to be gorge! with starch ; the 

 stoma remains open. The relative proportion of stomata to the number 

 of epidermal cells in a given area remains approximately constant in 

 the two cases. 



(4) The anatomical structure of the internal tissue of the leaves is 

 not materially altered. 



(5) The anatomical structure of the stem usually differs in the direc- 

 tion of the formation of less lignified xylem elements, fewer vessels, and 

 often also in the imperfect development of mechanical tissue. The phloem 

 shows no alteration. No alteration could be detected in the roots. 



Duration of Germinating Power of Seeds.* — Jules Poisson cites 

 certain observations which point to the retention of germinating power 

 for many years in marsh plants. In these cases the seeds have been 

 able to resist the action of moisture which is generally found to be preju- 

 dicial to the retention of germinating power. 



Irritability. 



Nature of the Stimulus causing the Change cf Form and Struc- 

 ture in an Amphibious Plant.f — W. B. McCalluin has tried to ascertain 

 the real factors which determine the type of leif produced by hetero- 

 phyllous water plants. The subject of his experiments was P 'roserpinaca 

 palustris, which grows in low swampy places usually flooded in spring 

 and early uummer, and subject to occasional submergence throughout the 

 season. He has studied seriatim as far as possible the effects of each 

 external factor, and concludes that the stimulus to the development of 

 the water form is not involved in the light relation, in the nutritive 

 conditions, temperature, the gaseous content of the water, nor the contact 

 stimulus of the water. The only factor which is constant in all cases 

 where the water form develops is the checking of transpiration, and the 

 consequent increased amount of water in the protoplasm. When the 

 latter is in that condition of dilution which accompanies the absorption 

 of a large amount of water, the nature of the growth is such as to 

 produce the water form, while those physical and chemical conditions 

 resulting from a partial withdrawal of water by evaporation (i.e. an 

 increased density of the protoplasm) result in the production of the 

 aerial form. 



Electrical Conductivity of Plant Juices.}-— F. D. Heald describes 

 apparatus and methods for the determination of the above. He finds 

 as the result of examination of the beet, potato, onion, radish, and four 

 other species, that plant juices are good conductors, the conductivity 

 being due largely to the dissolved mineral substances, while the organic 

 compounds play a minor part. The specific conductivity of the juice 

 obtained from the roots is always considerably less than that of the 

 juice from subaerial parts. The specific conductivity generally in- 

 creases progressively from the root upward, although in some cases the 

 sap from the stem has a higher conductivity than that from the leaves. 

 In the majority of cases the specific conductivity is a rough measure 

 of the relative amounts of ash present in different parts of the plant. 



* Comptes Eendus, exxxv. (1902) pp. 333-5. 

 t Bot. Gaz., xxxiv. (1902) pp. 93-108 (10 figs.). 

 X Tom. cit., pp. 81-92 (2 figs.). 



