NINTH LECTURE. 



IRRITO-CONTRACTILITY IN PLANTS. 



PROF. J. MUIRHEAD MACFARLANE, D. Sc. 



IN a paper published by me about nine months ago, I 

 showed that the generally accepted view that the leaf of 

 Dioiuza contracted after one stimulus of the irritable hairs was 

 incorrect, and that two stimuli were necessary to cause contrac- 

 tion. The other phenomena connected with leaf-closure, and 

 described in the paper, were so remarkable as to cause me to 

 inquire whether these phenomena were unique in the vegetable 

 kingdom, or whether conditions could be traced that connected 

 Dioncea with other sensitive plants. 



The behavior of the leaf of Dioncza to mechanical stimuli 

 given at varying intervals of time was such as to suggest a 

 very definite and exact contraction of the protoplasm of certain 

 cells. The outcome of the inquiries which are epitomized in 

 the present lecture, and which I hope in time to bring forward 

 in extended form, proves that in the vegetable as in the 

 animal kingdom, we have to do with a true contractile 

 tissue. Further, among those higher plants that we are now 

 to study, this tissue is made up of cells, each consisting of an 

 irrito-contractile protoplasmic sac enclosing a quantity of sap, 

 and each cell is joined to neighboring cells by protoplasmic 

 processes that pass through minute pores in the common 

 cellulose membranes. 



In order to make clear the relation that is shown by many 

 sensitive leaves to environmental stimuli, it may not be inap- 

 propriate to indicate first the possible movements that such 

 leaves can perform, as generally stated in memoirs and text- 

 books on the subject. A plant of the common yellow sorrel 



