ZOOLOGY AND BOTANY, MICROSCOPY, ETC. ' 333 



following maturity ; but the seed may remain buried for some years' 

 before it germinates. In Euphrasia (sens, lat.) and Alectorolophus, 

 germination never occurs before the spring following maturity. 



The paper contains other interesting matter respecting flowering 

 parasites or hemiparasites. The author concludes from his observations 

 upon Ldthrsea and Odontites vema that the production of i'oot-suckers 

 (haustoria) is the result of chemical attraction exerted by nutritive host- 

 tissue. Summarising his conclusions from Euphrasia and Alectorolophus : — 

 1 . These so-called hemiparasites are not very selective in their choice 

 of a host. 2. The degree of parasitical dependence varies with the 

 species. 3. The greater the degree of dependence, the less active the 

 formation of root-hairs. 4. The actual parasitism consists in the absorp- 

 tion of nutritive salts (Valimmt primitif) from the host-roots. The 

 leaves of green parasities are usually highly differentiated morphologically 

 and anatomically, and these plants need ample illumination, being highly 

 active in photosynthesis. In the case of the ephemeral Tozzia alpina, 

 however, the assimilatory tissue is very imperfectly differentiated, and 

 photosynthetic power much reduced in consequence. 



Change in Direct Sunlight during its Passage through Foliage.* 

 J. Wiesner has made further investigations concerning the relations 

 between plants and sunlight, with interesting results. The author finds 

 that while diffused light is of the highest importance to plants, and 

 direct sunlight never reaches the leaves as such, there are various adapta- 

 tions for protection against direct light, and for making the best possible 

 use of it. The latter is especially noticeable during cold seasons and in 

 cold climates. The present work shows that plants reduce the strength 

 of direct sunlight so as to obtain full benefit from it, in two different 

 ways : first, through the formation of sun-pictures, and secondly, through 

 a dispersing of the light in the leaves themselves. Sun-pictures are 

 formed by the passage of the light through the spaces in the leaves, and 

 the intensity of the light is in inverse ratio to the square of the distance 

 penetrated. Sun-pictures produced by small gaps are equally illuminated 

 over their whole surface, while those produced by larger gaps have a 

 greater intensity of light at the centre and less towards the outer limits 

 of their surface. When the large leaves of trees overlap so as to shut 

 off the light from the lower leaves, this disadvantage is overcome by the 

 formation of pinnate leaves which allow of the formation of sun-pictures 

 on the lower leaves. When the leaves are most numerous and diffused 

 light is thus largely cut off from the lower leaves, then is the conversion 

 of direct sunlight into diffused light through the formation of sun- 

 pictures most in evidence. The above only applies to plants with 

 numerous leaves. Plants having only few leaves rely upon the surround- 

 ing trees and shrubs for regulation of their light-supply. The cell- 

 contents themselves play an important part in converting direct sunlight 

 into diffused light. 



Respiration of Vegetative Organs of Vascular Plants.j — G. Nicolas 

 has studied the normal respiration of the vegetative organs of a large 



* SB. k. Akad. wiss Wien, cxviii. (1909) pp. 759-812 (11 figs.), 

 t Ann. Sci. Nat. Bot., s. (1909) pp. 1-113. 



