76 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Keasons are also given for thinking that the exposure to air is not 

 an important factor in the above changes. These and other con- 

 siderations show that though this permeation of the wall cannot be 

 accepted as proved as yet in any one case, still the subject deserves 

 more close attention than it has yet received, while it may be expected 

 that the application of new methods may produce definite results 

 bearing on this very important question. 



Intercellular Connection of Protoplasts.* — W. Hillhouse gives 

 the results of a large number of observations to prove the inter- 

 cellular connection of protoplasm. Out of twenty-two plants ex- 

 amined, these connections were only found in the cortical tissue of 

 Ilex Aquifolium and ^sculus hippocastanum, the pulvinus of Prunus 

 laurocerasus, and the winter bud pith of Acer pseudoplatanus ; he, 

 however, points out that these connections are easily broken in 

 preparation, and that a single connection between a number of cells 

 would be sufficient to produce a perfect unity of action. His con- 

 clusions are : — 



1. That protoplasmic threads connecting neighbouring protoplasts 

 are present in such widely different and diffused structures as sieve- 

 tubes, cortical parenchyma, leaf-pulvinus, pith of resting leaf-bud, and 

 endosperm of seeds. 



2. That in the contraction of the protoplast in natural plasmolysis 

 these threads would normally remain unbroken. 



3. That they may serve to transmit impulses from one cell to 

 another, acting in this way somewhat like a nervous system. 



4. That besides the perforating threads, equally widely spread 

 and much more numerous, are threads which attach the protoplast to 

 the cell- wall, whether at the base of pits or otherwise, and that these 

 threads are often opposite each other. 



5. That the closing membrane separating two threads often shows 

 differentiation, which suggests permeability, if not " sieve-perforation." 



6. That in the contraction of the protoplast in natural plasmolysis 

 these threads would naturally be unbroken. 



7. That these threads may, when in extension, act upon the cell- 

 wall and put it in a state of slight positive tension. 



8. That the presence of minute perforations communicating from 

 cavity to cavity of living cells would not, and when communicating 

 with the intercellular spaces need not, be a hindrance to the turgidity 

 of the cells. 



Polyembryony of Trifolium pratense.f — B. Jonsson describes 

 a case of polyembryony in the common red clover. He regards it 

 as arising, not from the presence of several embryo-sacs, but from 

 the formation of more than one ovum-cell iu the embryo-sac. 



Mechanical Structure of Pollen-grains.:]: — J. Vesque states that 

 pollen-grains shrink from evaporation of water ; those of a spherical 



* Proc. Brit. Assoc. Adv. Sci., 1883. Cf. Nature, xxix. (1883) p. 582. Cf. 

 this Journal, iii. (1883) p. 524. 



t Bot. Notiser, 1883, pp. 135-7. See Bot. Centralbl., xvi. (1883) p. 171. 

 % Comptcs Rendus, xcvi. (1888) pp. 1684-6. 



