Out of curiosity, I unearthed the following tidbit. Numerous peoples far more primitive than the Chinese figured out poison and darts and arrows; it seemed the Chinese would have, too.

Baicao, literally, 'white grass' or 'white herb.' It is identified in CICA, p. 85, n. 89 as being either the common bittersweet or woody nightshade (Solanium dulcamara L.), or the creeper Ampelopsis serianaefolia, "identified by the Japanese as the sorrel vine." However, I can find no evidence that either of these plants has ever been used to make arrow poison, although the woody nightshade is, of course, poisonous.
       It seems far more likely that it refers to one of the several aconite species (also known in English as monkshood or wolfsbane) that are commonly found across Europe and Asia. They are known to have been used as arrow poisons right up until modern times amongst the Ainu in northern Japan, and the Minaro in Ladakh (Peissel, Michel, 1984: 99-100). They were also used as a poison in the region of Lake Issyk-kol in modern Kyrgyzstan (St. George, George, et al. 1974: 167, 170).
       The Chinese were quick to make use of their knowledge of arrow poison. We find in the Biography of Geng Gong in Chapter 49 of the Hou Han shu that in 75 CE:

"The Xiongnu then conquered and killed Ande, the king of the Further Tribe. Then they attacked the town of Qinpu (near Guchen). (Geng) Gong climbed onto the ramparts, and led his soldiers into battle. He coated his arrows with a poison, and spread the rumour among the Xiongnu that the Han had sacred arrows, and the wounds of those who were hit would certainly be extraordinary. Then he used powerful crossbows to shoot these arrows. The barbarians who were hit noticed that their wounds were all frothing up. They were very frightened then.
...
The baicao of the Hou Han shu must surely refer to one of the wild species of aconite which were used to prepare arrow poisons and are reported as being abundant in the mountains surrounding the Tarim Basin. The following Chinese account from the 17th century briefly describes how they were prepared:

"In making poison arrows for shooting wild beasts, the tubers of wild aconitum are boiled in water. The resulting liquid, being highly viscous and poisonous, is smeared on the sharp edges of arrowheads. These treated arrowheads are effective in the quick killing of both human beings and animals, even though the victim may shed only a trace of blood." Sung (1637), p. 267.