That plant is the belladonna, or deadly nightshade.

Its alkaloid is a narcotic poison." Sauciness turned pale.

"I--have--just--eaten--some!" And began to whimper.

"O dear, what shall I do ?" Then did it, i.e.wrung her small fingers and cried.
"Pardon me one moment." Little passed his arm around her neck, and with his thumb opened widely the patrician-veined lids of her sweet blue eyes.

"Thank Heaven, there is yet no dilation of the pupil; it is not too late!" He cast a rapid glance around.