992 SUMMARY OF CURRENT RESEARCHES RELATING TO 



p. Physiology.* 

 (1) Eeproduction and Germination. 



Pollination of Pleurotliallis ornatus.f — Mr. F, W. Oliver describes tho 

 peculiarities of tlie structure of the flower of this orchid. Each sepal is 

 fringed with a row of cilia rendered vibratile by their very narrow base, and 

 conspicuous from containing nothing but air. Their swaying backwards and 

 forwards with every breath of wind renders them much more conspicuous to 

 visiting insects. The labellum is small, and moves narrowly on its narrow 

 neck when touched. Being quite hidden, this motion cannot be for the pur- 

 pose of rendering the flower more conspicuous, as in the case of some other 

 orchids, but appears to insure the insect's head being thrust against the 

 stigma or poUinia. 



(2) Nutrition and Growtli. 



Conditions of Assimilation.^ — Dr. N. Pringsheim communicates a pre- 

 liminary account of his researches on the dependence of assimilation in 

 green cells on the liberation of oxygen, and on the locality within the cell 

 where the oxygen formed in assimilation actually originates. He notes the 

 limitations of the prevalent method of gas analysis, and has striven by direct 

 observation of the protoplasm to determine the seat and relations of the 

 various functions. It seemed likely that the observation of protoplasmic 

 movements in varying conditions of light and darkness, and in partial or 

 total removal of oxygen, would afford a suitable starting-point for his 

 researches. Previous experiments had forcibly suggested that observed 

 differences in the assimilative energy did not in any way depend on dif- 

 ferences in the number of chlorophyll-bodies, nor on the abundance of 

 chlorophyll within these, but on the oxygen respiration of the protoplasm. 

 This point Pringsheim sought further to investigate. 



It has been known for long the green cells can break up carbonic dioxide 

 in the absence of oxygen, where the carbonic dioxide is mixed with some 

 innocuous gas. It is also known that protoplasmic movement is dependent 

 on the presence of oxygen. If this be so, the protoplasmic movement in a 

 green assimilating cell, in a medium free from oxygen, should not come to 

 a standstill as long as it is illuminated, and the conditions of carbonic acid 

 analysis fulfilled. With these facts in view, Pringsheim tried by experi- 

 ment to answer the question whether a plant normally assimilating would 

 cease to assimilate, without any alteration of the chlorophyll relations, if it 

 were deprived, even for a short time, of the oxygen which is essential for 

 respiration and plasmic movement, and whether it would recommence to 

 assimilate whenever fresh oxygen was supplied. His experiments answered 

 this in the af&rmative. 



The naked terminal cells of Chara leaves were placed in suspended drops 

 in a microscopic gas-chamber ; oxygen was as far as possible excluded ; a 

 continuous stream of carbonic acid and hydrogen passed through ; and the 

 amount of light caused to vary. In darkness the rotation of the protoplasm 

 gradually ceases, the length of time before stoppage varying with the degree 

 to which oxygen is successfully excluded, with the specific nature of the cell, 

 and with the mass of the protoplasm. The final result is a state of complete 

 "asphyxia," when the cell is dead, though still normal morphologically. 



* This subdivision contains (1) Eeproduction and Germination ; (2) Nutrition and 

 G-rowth ; (3) Movement ; and (i) Chemical Changes (including Respiration and 

 Fermentation). 



t Nature, xxxvi. (1887) pp. 303-4 (4 figs.V 



X SB. Preuss. Akad. Wiss. Berlin, 1887, pp. 763-77, and Ber. Deutsch. Bot. Gesell. 

 V. (1887) pp. 294-307. 



