Basket makers
Leeuwenhoek came from a family of basketmakers on his father's side. Although, according to Leeuwenhoek biographers Schierbeek and van Seters, Antony's grandfather Thonis Philpsz. (?-1643), was a basketmaker, as was Thonis's brother Cornelis Philpsz. (?-1616).
After that, the information is based on public records of baptisms and burials (assuming births and deaths in the same year). Thonis had only two surviving children, both sons, also basketmakers, Philips (?-1638) and Huijch (Hugo, ?-1669), Antony's father and uncle.
Hugo's older son, Lambrecht (1624-1701) was a basketmaker. Lambrecht's older son, Maarten (dates unknown), was a basketmaker, as was Maerton's son Pieter (1693-1750).
In short, most of the adult males in Leeuwenhoek's extended family were basketmakers, his grandfather, grand-uncle, father, uncle, two cousins, and three second-cousins.
The baskets were used to package non-liquid material for shipping. A prime example is all of the porcelain coming out the the Delft factories. Most of it was exported and had to survive the vagaries of travel in the 17th century.
The baskets were made from willow branches and reeds. The examples on this page both look like they have willow for the spokes or staves as well as for the weavers between them making up the sides of the basket.
While the baskets seem to have been woven one at a time, the size of Leeuwenhoek's father's house on the Oosteinde suggests that he employed several people.
In some industries, such as weaving fabric, the piece work was done at home and delivered to the merchant. In other industries, such as brewing and porcelain making, the workers came to the factory. Basket weavers needed only a board and a supply of willow, but that supply had to be steady.
Today, willows are cultivated with a system of short rotation coppicing (grienden), which lets a small area of land continually produce willow suitable for baskets. The land that Leeuwenhoek's family owned just over the singel from the house on the Oosteinde would have been appropriate (wet and close) for this purpose.
The willow trees are truncated or pollarded (knotten). The shoots that grow the following year tend to be the long and straight size best suited for basketmaking. The technique is common for landscaping effects but certainly adaptable for producing a steady supply of willow.