ON TROPISMS 59 



Grew performed a few experiments, especially in the direction 

 of plant chemistry. This was a natural line of work for a doctor, 

 since the extraction of various vegetable substances had long 

 been practised in medicine. He noticed, amongst other points, 

 that the green infusion obtained by treating a plant with olive 

 oil would, at least in the case of certain aromatic plants, appear 

 of a green colour in a small drop, but of a red, or deep yellow, 

 when a quantity of it was held up against a candle. In other 

 words, Grew seems to have observed the characteristic fluorescence 

 of chlorophyll. 



He was interested also in the subject of geotropism, and 

 succeeded in proving that there is an innate tendency for the 

 root to grow down and the stem to grow up ; and that it is 

 not merely a case of the root seeking the soil, and the stem 

 the air. His directions for performing the experiment are as 

 follows : " Take a Box of Moulds, with a hole bored in the 

 bottom, wide enough to admit the Stalk of a Plant, and set it 

 upon stilts half a yard or more above ground. Then lodg in 

 the Mould some Plant, for Example a Bean, in such sort, that 

 the Root of the Bean standing in the Moulds may poynt upwards, 

 the Stalk towards the ground. As the Plant grows, it will 

 follow, that at length the Stalk will rise upward, and the Root 

 on the contrary, arch it self downward. Which evidently shews, 

 That it is not sufficient, that the Root hath Earth to shoot into, 

 or that its Motion is only an Appetite of being therein lodged, 

 which way soever that be : but that its nature is, though within 

 the Earth already, yet to change its Position, and to move 

 Downwards. And so likewise of the Trunk, that it rises, when 

 a Seed sprouts, out of the Ground, not meerly because it hath 

 an Appetite of being in the open Aer; for in this Experiment it 

 is so already; yet now makes a new Motion upwards." 



Although Grew cannot be called a great experimenter, he 

 frequently took the easier course of throwing out suggestions 

 for such work. " The generation of Experiments " he describes 

 as " being like that of Discourse, where one thing introduceth 

 an hundred more which otherwise would never have been 

 thought of." Amongst other proposals he recommends that 

 trial should be made of growing plants in common water, snow 



