As in the evolution of many things, there is usually one who is the "spark" to prepare the way. Zaccharias Janssen was just one of the many building blocks needed. Had he not been inquisitive and inventive, it would have been possibly a lot longer before scientists of the day put together the idea of placing more than one lens in a tube. His works sparked the curiosity of other men such as Galileo to add to and improve upon his own findings. So Janssen was not directly responsible for cell theories. However, others such as Robert Hooke would not have had the platform to work from to develop a cell theory.