极环星系是种稀有的星系类型，它们有着几乎和银盘平面垂直，呈环形公转的大量的恒星、气体和星尘。
A rare galaxy type, polar ring galaxies have a substantial population of stars, gas, and dust orbiting in rings nearly perpendicular to the plane of the galactic disk.
研究表明，向日葵列当寄生严重度与向日葵的花盘直径、千粒重、盘粒重均呈现极显著的负相关；
The results showed that: 1) there was a significant negative correlation between parasitic severity of O. cumana W. and diameter of flower dish, weight per thousand seeeds or weight per dish;
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