23 



V. — On the Structure of some Tissues possessing Hygrornetric 

 Properties. By E. J. Quekett, F.L.S., F.B.S., &c. 



Read November 25, 1840. 



The observations contained in the following communication, will 

 be found to have reference to the effects of moisture and dryness in 

 causing various alterations in the form and conditions of many of the 

 organs of plants, in the recent as well as in the dry states ; and also 

 it will be attempted to be shown that there is some peculiar structure 

 and arrangement of the tissues in those parts where these effects are 

 most manifest. 



That there are hygroscopic properties in the tissues of plants can- 

 not be doubted ; and that these properties are not universal through- 

 out the vegetable kingdom is also evident, by the fact being shown 

 only in plants of particular orders, and in particular parts of various 

 plants of all orders. As this quality is not general but special, it 

 must be regarded in the light of an attribute of the plants so endowed 

 by which they are enabled to exercise particular functions through 

 this property, which are of essential importance in their economy. 



Numerous are the instances where the abstraction from, and the 

 addition of water to, portions or to some entire plants, exerts singular 

 effects, which are found to be occasionally the very opposite in one 

 part to that which happens in another ; for instance, the application 

 of moisture will cause a contracted portion to expand, and it will also 

 cause a closed organ to open : the drying of the tissues will also ef- 

 fect the same changes, causing some organs of plants to open, and 

 those which moisture opens to contract. 



Instances of the first effects are very readily witnessed in the moss- 

 es, which, notwithstanding they may have been dried and shrivelled 

 for very many years, yet when moistened they put on the appearance 

 and characters of living specimens ; some have even supposed that 

 life is not extinct in these plants, after many years have been passed 

 in this dry condition. There can be no doubt that this hygroscopic 

 property of the tissues of mosses is a special provision, as they are 

 destined to be in perfection in the winter months, and ripen in that 

 season the means for their propagation ; so that in the summer 

 months, when the increased temperature quickly evaporates the mois- 

 ture from their delicate cellular tissue, they shrivel and wither, yet 

 they do not perish ; but on the first rainy season of autumn they ra- 

 pidly absorb the moisture that falls upon them, their tissues becom- 



