Moore R, Pasieniuk J
Department of Biology, Baylor University, Waco, TX 76798, USA.
Can J Bot. 1984;62:1767-9. doi: 10.1139/b84-239.
After branching from the primary root, secondary roots of castor bean (Ricinus communis) grow laterally for 15-20 mm, after which they bend downward (i.e., become positively gravitropic). During the first 10 mm of growth, the lengths of caps of secondary roots increase from 120 +/- 26 to 220 +/- 28 micrometers. Although this increase is statistically significant (P < 0.1%), the resulting secondary roots are only minimally graviresponsive. A subsequent doubling of the lengths and widths of the root caps (i.e., to 420 +/- 34 and 450 +/- 41 micrometers, respectively) is positively correlated with the onset of gravicurvature. The graviresponsiveness and dimensions of caps of positively gravitropic secondary roots are not significantly different from those of positively gravitropic primary roots. These results indicate that (i) a statistically significant increase in the length and length : width ratio of a root cap does not necessarily result in the root becoming positively gravitropic, (ii) there may be a minimum cap length and (or) width necessary for graviresponsiveness, and (iii) the degree of graviresponsiveness exhibited by a particular root may be related to the size of its root cap.
蓖麻（Ricinus communis）的侧根从主根分支后，会横向生长15 - 20毫米，之后向下弯曲（即变为正向地性）。在生长的最初10毫米内，侧根根冠的长度从120±26微米增加到220±28微米。尽管这种增加具有统计学意义（P < 0.1%），但由此产生的侧根仅具有最小程度的重力响应。随后根冠的长度和宽度加倍（即分别达到420±34微米和450±41微米）与重力弯曲的开始呈正相关。正向地性侧根根冠的重力响应性和尺寸与正向地性主根的没有显著差异。这些结果表明：（i）根冠长度和长宽比在统计学上的显著增加不一定会导致根变为正向地性；（ii）可能存在重力响应所需的最小根冠长度和（或）宽度；（iii）特定根所表现出的重力响应程度可能与其根冠大小有关。
