The diver strapped the aqualung to his back in preparation to dive
The two subjects of the sentence are Colonel Lloyd and his "finely cultivated garden".
In the very, very simplest terms, judging the validity of an argument starts centers around this process:
1) Identify the rhetoric (Lines of Argument) from the actual, formal reasons. Separate the persuasive language from the actual claims to truth and fact.
2) Analyze those reasons (claims to truth and fact) by identifying their logic (often in the Implicit Reasons) and evidence.
3) Test and evaluate the logic and evidence; identify logical errors and ask whether the evidence can and has been tested and objectively, repeatedly, factually verified.
