Mr. Valentine on the existence of Stomata in Mosses. 243 



hiscence is prevented from falling on account of its adhesion with the colu- 

 mella (a common occurrence), which may be a sufficient provision against the 

 premature dispersion of the sporules ; or even the tissue in some cases may be 

 so lax in its disposition as to allow of the action of the atmosphere on the 

 internal organs : and I am disposed to believe that this takes place to a con- 

 siderable extent, from witnessing the presence of green granules in tissue 

 which appeared to have no communication whatever with the air, and from 

 being frequently puzzled to decide whether certain double lines on the cuticle, 

 formed by the walls of two neighbouring cells, are stomata or not ; they cer- 

 tainly often appear as competent to perform the imputed function of stomata 

 as the stomata themselves. Although the cause of the green colour of the 

 granules is light, I think I am right in giving the atmosphere a share in the 

 process, for from what other source is the carbon on which the light acts de- 

 rived ? In addition, the theca of Phascum alternifolium is thinner and more 

 transparent than that of any other moss, and it is well known that the tissue 

 of mosses is of all other plants the most easily permeable by water, the per- 

 meability being in fact so perfect as to make the presence of stomata as 

 exhalants unnecessary ; and, finally, stomata are not found in a single instance 

 on the organs of vegetation. So much for what is as yet but a conjecture. You 

 will observe that I have assumed the hardening to be caused by the influence 

 of the atmosphere. 



The development of the stomata will be an interesting subject for investi- 

 gation : all I at present know of the matter is, that in the young state they 

 are very small and much less numerous than when the theca has arrived at 

 maturity ; for instance, the average number on the theca of Orthotrichum dia- 

 phanum, when mature, is from twenty to five and twenty, whilst on the very 

 young theca 1 have found as few as five, and these were like ordinary stomata, 

 the projecting cells in that early stage not having been developed. 



I have some hope that I shall be able to turn these stomata to good ac- 

 count in the arrangement of genera. If I succeed, you shall have the facts in 

 a future letter. I have not yet actually begun my work. I am collecting 

 material which grows almost daily. I shall soon begin a series of drawings 

 illustrating the development of some common moss in all the stages of its 



