532 Allgemeines. — Anatomie. 



this may be considered doubtful. The total amount of incident 

 energy seems to be equivalent to 1 — 3 calories per sqr. cm. 

 per min., and by a consideration of the amount of Chlorophyll 

 in a sqr. cm. of leaf — it being shown that this substance is 

 present as a thin external layer in the chloroplast, we arrive 

 at the astounding result that if the whole energy absorbed by 

 the Chlorophyll be retained without re-radication the tempera- 

 ture that could be realized in a minute in the layer of Chloro- 

 phyll is about 6000° C. — a figure of the same order as that 

 required for the disentegration of carbon dioxide in the labora- 

 tory. Probably as suggested by Wiedemann, there is here 

 a process of chemiluminescence or the direct transformation of 

 radiant energy into chemical work without the intermediate 

 stage of a high temperature. When the carbon dioxide is 

 absent the radiant energy which can no larger be transformed 

 into chemical work is probably used in the process of chloro- 

 vapourisation. The result of the relegation of the Chlorophyll 

 to a thin layer on the outside of the chloroplasts is that it 

 occurs in a nearly solid form and this would account for the 

 very small degree of fluorescence exhibited by living green 

 Organs. E. Drabble (London). 



B00DLE, L. A., On theOccurrence ofSecondary Xylem 

 in Psllotum. (Annais of Botany. Vol. XVIII. No. LXXI 

 p. 505. 1904.) 



The author finds that a certain amount of secondary xyiem 

 is formed in the subterranean Stocks of the aerial shoots of old 

 plants of Psllotum triquetrum, and also at the base of the 

 aerial shoots themselves. The secondary tracheides are scala- 

 riform, or irregularly pitted, and frequently take a sinuous 

 course, probably owing to sliding growth. They are smaller 

 than the tracheides of the primary xylem, and occur between 

 the latter and the ring of sieve-tubes. They are formed consi- 

 derably Iater than the primary xylem, and shew a successive 

 and somewhat irregulär developement. There is no definite 

 cambial layer, but indications of radial arrangement are fre- 

 quently found in the secondary tracheides and the surrounding 

 parenchyma. 



The production of the secondary tracheides in the sub- 

 terranean parts is regarded as due to a basipetal Stimulus from 

 the aerial shoots. They are held to represent reduced se- 

 condary xylem, and the author points out how striking a re~ 

 semblance to structure of a young stem of Sphenophyllum is 

 given by their presence around a triarch primary xylem, such 

 as occurs in some parts of the stem. In the lower region of 

 the aerial stem a few cases were observed in which the proto- 

 xylem apparently took up a mesarch position. 



D. J. Gwynne-Vaughan. 



