The only useful text I could find on it:
In 1755, Benjamin Martin had promoted, in his General Magazine of Arts and Sciences, a proposal for 'perpetually electrifying the Plants and Fruit Trees of an artificial Garden'. He argued that as electricity is now well known to be somewhat more than a Matter of mere Curiosity, inasmuch as it has been successfully applied to the Cure of several Disorders of the rheumatic and paralytic kind … also it is well known greatly to promote Vegetation in Plants; and doubtless may be found of use in many other cases, if it were applied in a Proper Manner, I mean so that it might be rendered constant or perpetual, and not momentary and instantaneous, as in the common Way of using it. 16 Thus, he proposed a machine with two glass globes generating a constant supply of electricity to stimulate an irrigated garden (see Figure 5). While Martin's proposal seems never to have been realized, by the 1790s, Erasmus Darwin was expressing a well-accepted opinion when he noted that 'the influence of electricity in forwarding the germination of plants and their growth seems to be pretty well established'.
Taken from this link: https://www.researchgate.net/figure/A-Machine-for-a-Perpetual-Electrified-Garden-from-The-General-Magazine-of-Arts-and_fig5_322717384
So it would seem based on these words that the machine in the image was never actually made. Though I am curious to know how two glass globes generate a constant supply of electricity?
wow. there seems to be so much we do not know and will have to re-member.