84 SUMMARY OF CURRENT RESEARCHES RELATING TO 



In the parenchyma of the pith the most beautiful examples are 

 furnished by the Lorauthaceae. In the Coniferfe it can only be shown 

 in young twigs, as in Salishiiria ; while in Abies alba a connection 

 among the cells of the medullary rays, between these and the bast- 

 parenchyma, and in the sclereuchymatous cells which bound the 

 xylem, can be directly made out. In the bast-fibres the connection 

 is more difficult to determine ; it occurs in Visciim and in ConifcrcB. 

 In the elements of the soft bast it is particularly well marked, 

 especially in the sieve-vessels. 



In the cambium it is very difficult to determine, and the author 

 has at present made it out only in tlie Coniferfe. 



The connection of the elements of the xylem can be detected 

 especially in the Loranthaceaj ; in Coniferai it has been observed in the 

 trachoids of Salisburia. In the wood-vessels none has yet been 

 observed. 



Secreting cells invariably manifest continuity : for example, the 

 resin-passages in Coniferte ; and the same is true of the protoplasmic 

 envelope of clusters of crystals. 



Intercellular protoplasm is always in connection with the cell- 

 ])rotoplasm, and was found by the author not only in collenchymatous 

 and parenchymatous tissues, but also in typical prosenchyma. It 

 may even contain chlorophyll, and intercellular spaces may develope 

 into true cells ; it always occurs between the cells of parenchyma 

 rich in protoplasm, but not between thin-walled cells containing but 

 little protoplasm. It often occurs as a layer between the cell-walls 

 of adjacent cells, and forms, in fact, a mantle euiTOunding the cells, 

 and passing into the intercellular spaces. Good examples of the 

 development of these intercellular spaces into cells, w-hich takes place 

 with very great rapidity, occur in the collenchymatous cortex of 

 Ficus elastica, and in the xylem, between the wood-cells and the 

 vessels, of Rhus cotinus. The formation of new cells in this way is of 

 very great importance in the vegetable economy, and gives rise to 

 fresh development of intercellular spaces. 



The author suggests that the origin of this intercellular proto- 

 plasm may be that particles of cytoplasm become inclosed within the 

 young cell-wall, which still remain in connection with the proto- 

 plasts ; and that a layer of protoplasm which is found between the 

 layers of adjacent cells may be the remains of the cell-plate. 



Intercellular Relations of Protoplasts.* — W. Hillhouse gives a 

 very useful epitome of the observations at present made on this 

 subject, including his own researches. The paper contains a minute 

 account of the structui-e and development of sieve-tubes and sieve- 

 plates. 



Plasmolysis-t — H. de Vries points out the importance of plasmo- 

 lysis, or the separation of the living protoplasm from the cell-wall by 

 desiccating solutions, in the study of physiglogical phenomena. He 



* Midland Naturalist, vii. (1884) pp. 61-6, 101-5, 121-6 (1 pi.), 

 t Bot. Ztg., xlii. (1884) pp. 289-98. 



