88 pringsheim's researches on chlorophyll. 



rays occupying middle of the solar spectrum, having wave- 

 lengths between -00060 — -0004:5 mm. ; and in blue light 

 (fig. 28, spectra i, k), produced by a 5 — 6 mm. thick solution 

 of ammonia copper sulphate, giving passage to the strongly 

 refractive rays of vvave-lengths from '00051 and -00053 mm., 

 after fifteen to twenty minutes' exposure the temperature 

 rose, even when the original temperature in the drop was 

 20° — 25° C, to only 35° — 36° C, — a degree in no way 

 hurtful to plant cells. 



Green and blue are thus the most favourable for investi- 

 gations with intense light, as in them the effects are strictly 

 photochemical. 



III. Effect of Light. Paralysis and Death from Light. 



A. Concerning the appearances produced in Plant Cells by 

 the action of Intense Light. — The time which elapses before 

 visible effects appear in a cell exposed to intense light 

 varies according to the specific energy of the cell. In 

 most plants, and without exception in green plants, a few 

 minutes suffice for their appearance, and the extent of the 

 action can be regulated so that transformations may be 

 brought about in the cell content without injury to the life 

 of the cell, or paralysis and death of the cell may be pro- 

 duced. Some cells, however, especially non-green ones, for 

 example, colourless swarm-spores which are very sensitive 

 to heat, are but slightly affected and may remain for half- 

 an hour or more exposed to ^ concentrated white light 

 without injury, — an important fact, as showing that a 

 cell is not of necessity killed or iiijured when exposed in 

 water to the heat which is generated in the focus of a 

 large lens. 



For investigation of the effect of intense light on green 

 tissues, Alg<s, Characece, moss leaves, hairs and soft leaf- 

 tissues of Fluviales, are favourable subjects, as in them the 

 effect is generally ap))aient in from two to six minutes. 



If species of Spirogyra, such as nana, jugalis, quinina, or 

 Webcri, be exposed to intense light, the effect immediately 

 observed is complete disappearance of colour from the 

 chlorophyll-bands. The ground-substance remains un- 

 changed in form and disposition, and the marginal jnojections 

 and amylum-bodies persist (fig. 19 a, b, c, d). The band 

 appears as if acted upon by alcohol, and the decolorisatiou 

 is limited to the insolated area, though at times there may 

 be a slight halo. It is possible to restrict the action of 

 the light to one coil of the chlorophyll-band or to a 

 portion of it, or, if a plant be employed with isolated 



