Another scientific mission in the 1960s gave Zeng a rare opportunity to get closer to nature. He was assigned to draw potential anti-malaria herbs in dense forests in the border areas of Yunnan, which were submitted to research institutions.

　　"I was so excited and forgot everything while painting. I even couldn't notice the insects around me. I once got 42 bites from leeches and only found out the next morning when my body was tightly stuck to my bed with blood," Zeng said.

　　The magnificence of nature stunned him and inspired him to make painting nature his lifetime endeavor.

　　Following his retirement in 1997, Zeng embarked on a new journey – depicting plants and animals in a more artistic way. He spent several years absorbing more painting techniques from both traditional Chinese and modern Western.

　　Compared to the illustrations that stress the plants' scientific use, Zeng said his works now focus more on their aesthetic value.

　　"But when it comes to 'beauty,' it's actually different from the mainstream concept. My works are based on certain professional knowledge. It means that I first need to know which family and genus a plant belongs to and its morphological characteristics," Zeng said.

　　Giving an example, he said azaleas with 10 stamens belong to different genus from those with five stamens and so he needs to paint them as they are.

　　In recent years, he has published hundreds of works, which have been presented in exhibitions and books and on stamps.

　　One of his latest masterpieces is a giant painting specifically for the International Horticultural Expo underway in Beijing. Titled "The Journey of Chinese Plants," it features 37 plants which originally grew in China and then spread around the world.

　　"To finish such a large painting in a short period of time, I had no time to prepare a draft and draw them in the wild. So, I could only work based on my experience," said Zheng, adding that it's a big challenge for him given his age.

　　"Sometimes when I finish a whole day's work, I would shiver all over," he said. "I've painted almost all my life, and still have the chance to contribute a little to the great event. I think it's my honor."

　　Looking ahead, Zeng plans to continue to "praise nature and life" with more paintings as long as his health holds out.

　　"What worries me most is that I would be too weak to hold my paintbrush some day. There are still too many things for me to paint," said Zeng.

　　Besides the rainforests series, he is working on another project – painting plants recorded in the Classic of Poetry, or Shijing, the oldest existing collection of Chinese poetry.

　　Some of Zeng's works have been acquired by museums.

　　"I have never sold my paintings and will never do that," he said.

　　Despite success, Zeng remains humble and does refer to himself as an artist.

　　"I'm just a 'craftsman,' which means I will stick to doing one thing to the best, till the end," said Zeng.