Taken in by the stratagem of Rosa, who had feigned to put it in the ground, and entertaining no doubt that this little farce had been played in order to force him to betray himself, he redoubled his precaution, and employed every means suggested by his crafty nature to watch the others without being watched himself.
He saw Rosa conveying a large flower-pot of white earthenware from her father's kitchen to her bedroom. He saw Rosa washing in pails of water her pretty little hands, begrimed as they were with the mould which she had handled, to give her tulip the best soil possible.
And at last he hired, just opposite Rosa's window, a little attic, distant enough not to allow him to be recognized with the naked eye, but sufficiently near to enable him, with the help of his telescope, to watch everything that was going on at the Loewestein in Rosa's room, just as at Dort he had watched the dry-room of Cornelius.
He had not been installed more than three days in his attic before all his doubts were removed.
From morning to sunset the flower-pot was in the window, and, like those charming female figures of Mieris and Metzys, Rosa appeared at that window as in a frame, formed by the first budding sprays of the wild vine and the honeysuckle encircling her window.
Rosa watched the flower-pot with an interest which betrayed to Boxtel the real value of the object enclosed in it.
This object could not be anything else but the second bulb, that is to say, the quintessence of all the hopes of the prisoner.
When the nights threatened to be too cold, Rosa took in the flower-pot.
Well, it was then quite evident she was following the instructions of Cornelius, who was afraid of the bulb being killed by frost.
When the sun became too hot, Rosa likewise took in the pot from eleven in the morning until two in the afternoon.
Another proof: Cornelius was afraid lest the soil should become too dry.
But when the first leaves peeped out of the earth Boxtel was fully convinced; and his telescope left him no longer in any uncertainty before they had grown one inch in height.
Cornelius possessed two bulbs, and the second was intrusted to the love and care of Rosa.
For it may well be imagined that the tender secret of the two lovers had not escaped the prying curiosity of Boxtel.
The question, therefore, was how to wrest the second bulb from the care of Rosa.
Certainly this was no easy task.
Rosa watched over her tulip as a mother over her child, or a dove over her eggs.