72 SIXTEENTH CENTURY pt. hi. 



help to botanists, and would soon have led them to make 

 better systems if they had followed it \ but it was not gene- 

 rally adopted, and for nearly a hundred years longer many 

 went on in the old way, collecting and naming plants with- 

 out trying to classify them. Csesalpinus knew about 1,500 

 species of plants, 700 of which he had collected himself He 

 was the first to point out that the use of flowers which have 

 no seed-vessels but only stamens (or little thread-like stalks, 

 tipped with yellqjv powder), is to drop the powder or pollen 

 on flowers which have only seed-vessels and no stamens, 

 and by this means to cause the seeds to grow and ripen. 

 Such plants which have the stamens in one flower and the 

 seed-vessel in another are now called Dioecious plants. 



Chemistry of Paracelsus and Van Helmont, 1520- 



. 1600. — There is very little worthy of notice in the chemistry 



of the sixteenth century ; but we must mention in passing 



two famous men : Paracelsus, who was bom 1493 at Einsiedel 



in Switzerland, and Van Helmont, bom at Bmssels in 1577. 



Paracelsus was at one time Professor of Physic and Sur- 

 gery at Basle, but he gave up his professorship and travelled 

 about Europe during the greater part of his life. Among 

 other things, he pointed out that air feeds flame, and that, if 

 you put iron into sulphuric acid and water, a peculiar kind of 

 air rises from it. He also succeeded in separating gold out 

 of a mixture of gold and silver by using aquafo7-tis or nitric 

 acidj which dissolves the silver and lets the gold fall to the 

 bottom of the vessel. He did not, however, make many 

 ' discoveries which are valuable now, and he taught a great 

 deal that was absurd and bombastic. 



Van Helmont was also a wandering physician, but as a 

 chemist he was more careful in his experiments than Paracel- 

 sus. He seems to have known a great many different gases, 



