400 Prof. H. Marshall Ward. The Relations between 



The Host-plant, and the Behaviour of its Normal Tissues. 



I begin by briefly calling attention to the healthy tissues of a 

 normal green flowering plant, and we need only consider for the 

 moment what is going on in the parenchyma cells of a leaf or stem, 

 such as every one knows the anatomy of. In a selected piece of such 

 tissue we find the mass cut up into a number of thin- walled cham- 

 bers, the cells, each of which contains a lining of living, colourless 

 protoplasm, with strands or plates of the same running across ; in 

 this protoplasm are embedded the nucleus and the green chlorophyll 



Fig. 4. Portion of the cell-tissue of a higher plant, in longitudinal section and 

 highly magnified. Each of the cells is bounded by the cellulose cell-wall; and 

 this is lined by the protoplasm in which are embedded the nucleus (a — e) and 

 the green chlorophyll corpuscles {g — i). This protoplasm encloses the cell- 

 sap, and strands of the former may pass across (as at /), or plates of proto- 

 plasm may separate the sap of one part of the cell from that of another 

 (Kny). 



corpuscles. In the large vacuoles or sap-cavity of each cell is a clear 

 liquid, the cell-sap, consisting of water with small quantities of 

 mineral salts, dissolved gases, organic acids, and salts and other 

 crystalline and non-crystalline substances in various proportions at 

 different times.* Of course, I need not here enter into a long de- 



* On the subject of the extreme complexity of the cell-sap and protoplasm, see 

 Pfeffer, " Beitrage zur Kenntniss der Oxjdationsvorgange in lebecden Zellen " 

 ' Abhandl. Math.-phy;. Classe Sachsischen Gesellsch. d. Wiss.,' vol. 15, 1889, pp. 

 455—466). 



