INVESTIGATORS IN PHOTOSYNTHESIS 63 



tions and Experiments relating to Vegetation and Re- 

 spiration," and in it he describes how a friend of his, 

 Mr Walker (of English Dictionary fame), told him that, 

 while waiting for a boat to convey him to the continent, 

 he noted a horse trough at the principal inn at Harwich, 

 which the landlord refused to have cleaned out because 

 he found that its contents remained longer sweet when 

 the sides and bottom of the trough were "covered by 

 a green substance which is known to be of a vegetable 

 nature." After describing the " spontaneous emission 

 of dephlogisticated air from water containing a vegeta- 

 tive green matter " he says he " never found the 

 emission took place save when the water was exposed to 

 light." 



Sachs in his estimate of Priestley's work says : 

 " Priestley himself did not suspect that the deposit in 

 question, afterwards known as ' Priestley's matter,' and 

 found to consist of Algae, was a vegetable substance." 

 This is quite incorrect. In Section VII. of Book IX. 

 Priestley says that at first he supposed the green substance 

 to be a plant but " was unable to discover the form of one. 

 Several of my friends, however, better skilled in Botany 

 than myself, never entertained any doubt of its being a 

 plant ; and I had afterwards the fullest conviction that 

 it must be one. Mr. Bewley has lately observed the 

 regular form of it by a microscope. It will come most 

 properly under the denomination of the Conferva ; but 

 this not being within my province I shall not presume 

 to give it any particular appellation." It would appear 

 that Sachs had studied the works of Priestley with the 

 same care that he bestowed on those of Theophrastus 

 and Malpighi ! 



The seed sown by Priestley very soon bore fruit. 

 In 1730, three years before Priestley first saw the light of 

 day, there was born in Breda in Holland, Jean Ingen- 

 Housz, who was destined to become one of the founders 

 of plant physiology. After completing his university 



