by the aid of Polarized Light. 275 



nomena; but the green colouring matter is in a high degree 

 obstructive to the development of a bright light, as is shown by 

 the comparison of the chlorophyll of a leaf bleached by alcohol 

 with a fresh leaf of the same plant. 



In the granules of oleaginous seeds (Hartig's aleur on- granules) 

 I could usually find no sign of double refraction ; distinct traces 

 were, however, displayed, on the application of a plate of mica, 

 in the seed of Attalea funifera. 



In the primordial utricle I ordinarily found no trace of double 

 refraction. In the Spirogyrce, however, it exhibited, after con- 

 traction with weak alcohol, on the application of a plate of sele- 

 nite or mica, a very weak but quite evident reaction like that of 

 cellulose. 



My observations on the last three structures are, as is evi- 

 dent, very insufficient ; further improvements of the observing 

 instruments are required in order to arrive at decided results 

 respecting their behaviour with polarized light. 



The polarizing microscope, even in its present condition, is 

 excellently adapted for the discovery of crystals in plants, since 

 these appear with surprising brilliancy on the dark field. Al- 

 though it has been long known that crystals are very widely 

 difi'used formations in the vegetable kingdom, and that scarcely 

 a plant exists, in the higher orders, in which they may not be 

 discovered, — yet one is surprised, on the application of polarized 

 light, to find the crystals far more frequent, and in far greater 

 quantity, than one is accustomed to see on investigation with the 

 ordinary microscope. The quantity of them in many Lichens, 

 for instance in Lecanora tartarea, is quite surprising in amount ; 

 and they will likewise be found in the tissue of many embryos, 

 where they would otherwise easily escape notice on account of 

 their small size and the granular contents of the cells ; but even 

 in other parts where they have long been known and are more 

 readily discoverable, they may be detected more easily and in 

 greater quantity, and as crystals, in polarized light. I will 

 mention, in reference to this, only the stellate hairs of the air- 

 canals of NymphcBa, in each nodule of which lies a crystal, so- 

 luble in strong acid. The crystals mostly appear, even without 

 the application of a selenite- plate, in brilliant colours ; and there 

 is not a more attractive spectacle than the view of a great quan- 

 tity of [sulphate of lime ?] crystals in the petiole of many Mu- 

 sacese, e. g. Urania speciosa, or of the larger raphides, such as 

 are so common for instance in the tissues of the Aloes. Whe- 

 ther crystals occur which belong to the regular system, and 

 consequently do not act upon polarized light, is unknown to me, 

 but I have met with none hitherto. — (A. H.) 

 Tiibingen, November 1857. 



18* 



