170 , CORBESPONDENCE. 



nettle is not a true jelly, but consists of colls filled with fluid. On the 

 other hand, the crystalline lens of the eye, as Brewster observes, has a 

 strong action on polarized light when strained either by external 

 pressure or by the unequal contraction of its parts as it becomes 

 dry." 



Is the Lichen Solorina hispora a Distinct Species ? — Dr. J. Stirton 

 communicates a note to ' Grevillea ' (January, 1874), in which he 

 asserts that it is. He says : — " Since detecting this lichen for the first 

 time in 1871, on Ben Lawers, I have secured it on almost every 

 moimtain in Scotland that I have climbed, of a greater elevation than 

 3000 feet. Accordingly, so far as my experience goes, it is more 

 frequent than S. saccata, which is usually found, besides, at much 

 lower elevations — a fact which, in my estimation, ought not to be 

 wholly ignored in the question of specific distinction. In all these 

 instances (four in number) the thecfe are 2-spored, without exception. 

 Occasionally, it is true, a one-spored theca may be seen, where the 

 spore is larger than usual, viz. as in one specimen ( • 1 x ' 054 mm.), 

 but, as is well known, especially in the larger spored lichens, such a 

 state is easily accounted for physiologically, although the converse 

 does not hold true. Again, in S. saccata, 2-spored thecse are occa- 

 sionally though rarely seen in this coimtry, mixed with the 4-s25ored, 

 where such spores approach in configuration and, to a less extent, in 

 size those of S. hispora, but this fact, so far from militating against 

 the specific value of the latter, is, in my opinion, decidedly in its 

 favour, and is merely a counterpart of what (as we have stated) is 

 seen in its own internal organization. In this way is explained what 

 is described by Anzi, and distributed by him from time to time." 



COEEESPONDENCE. 



The Aperture Question. 



To the Editor of the ^Monthly Microscopical Journal.' 



London, Mco-ch 5, 1874. 

 Sir, — As Col. Woodward now appears to have fallen into the ranks 

 of my opponents, I hope he will excuse me for not offering explana- 

 tions on this question for his special consideration, as the arbiter by 

 whom the conditions might be set at rest : I have argued that he is 

 wrong in his optical demonstrations, therefore it would be out of cha- 

 racter for me to make excuse or apology for an offence that I may 

 at any time repeat ; and as his other remarks have been adverted 

 to, I shall confine myself to those on the diagram portion only, 

 leaving others to judge whether the phrases he applies to me, such as 

 " unfounded assiunptions " and " dogmatic assertions," * be altogether 



* Vide Col. Woodward's letter, ' M. M. J.' for March last, page 120. 



