Sentence:  It is said that the herb "Christswoort", or "Christmas flower", in plain English "Black Helebore", (so called from its springing about this time) helpeth madnesse, distraction, purgeth melancholy and dulnesse. This last expression minds me to <WSD>caveat</WSD> the Reader, not to be angry at Helebore because it's called "Christmas flowre"; for it, poore thing, hurts no body that lets it alone, ... [quoting V. Annand's "Mysterium Pietatis", pages 24–25.] 
Meaning of the word marked with <WSD> tags:  To warn or caution against some event.