Sentence:  At Hortus Bulborum you will find <WSD>heirloom</WSD> narcissi that date back at least to the 15th century and famous old tulips like 'Duc van Tol' (1595) and its sports. 
Meaning of the word marked with <WSD> tags:  An old crop variety that has been passed down through generations of farmers by seed saving and cultivation, in contrast to modern cultivars used in large-scale agriculture.