在二十世纪上半叶，苏联柑橘专家(Citrology在当时是一个重要学科)在-30℃的低温下在户外种植（亚）热带植物，而且不使用玻璃或任何燃料辅助。
During the first half of the twentieth century, Soviet citrologists grew (sub)tropical plants in temperatures as low as minus 30 degrees Celsius – outdoors, and without the use of glass or any fossil fuel-powered assistance.
"渐进式抗冻" “Progressive cold-hardening”
进口的柑橘品种只在黑海沿岸几个孤立的地方存活，那里的小气候特别有利。为了使柑橘类水果更好地适应寒冷，苏联的柑橘学家采用了一种叫做 "渐进式抗冻"的方法。这使他们能够创造出适应当地生态条件的新品种，这种栽培策略最初是为杏树和葡萄开发的。
Imported citrus varieties only survived in a few isolated points along the Black Sea coast, which enjoyed a particularly favourable microclimate. To better prepare citrus fruits for cold, Soviet citrologists followed a method called “progressive cold-hardening”. It allowed them to create new varieties which were adapted to local ecological conditions, a cultivation strategy which had originally been developed for apricot trees and grapes.
该方法包括将珍贵的树木种子种植在其原始位置的更北边，然后等待它结出种子。然后将这些种子再向北种植，并反复重复这一过程，缓慢但稳定地将柑橘品种推向不太适宜的气候。利用这种方法，Rostov-on-Don(北纬47°N的一座城市，挨着亚速海)的杏树最终可以在北方650公里以外的Michurinsk(北纬52°N)种植，他们在那里开发了适应当地气候的杏树种子。另一方面，直接将Rostov 杏树的种子种植在Michurinsk证明是不成功的。
The method consists of planting a seed of a highly valued tree a bit further north of its original location, and then waiting for it to give seeds. Those seeds are then planted a bit further north, and with the process repeated further, slowly but steadily pushing the citrus variety towards less hospitable climates. Using this method, apricot trees from Rostov could eventually be grown in Mitchurinsk, 650 km further up north, where they developed apricot seeds that were adapted to the local climate. On the other hand, directly planting the seed of the Rostov apricot tree in Mitchurinsk proved unsuccessful.
不要再吹儒家智慧了。无产阶级才是真的智慧。。。
~~这故事唯一的毛病就是 Rostov 和 Michurinsk 这城市的位置似乎弄反了？反正纬度没太对劲。。。~~
更新：原来是 Rostov-on-Don，不是 Rostov(北纬57°N的一座城市，莫斯科以北202km涅罗湖岸边)
另外「橘生淮南为橘，生淮北为枳」这句话本身也是错的
橘和枳原本就是两个根本不同的物种，在生物学特征中，橘与枳同属芸香科，虽枝、叶、果实形态相似，但枳比橘耐寒，可逾淮河而生。而橘喜温，逾淮河过了1月0℃等温线就会被冬天的霜雪冻死。所以，不是橘到淮北变成了枳，而是淮北只有枳而无橘。