这篇文章在复述段意的时候特别扭：还请大家指正，谢谢：
All of the cells in a particular plant start out with the
same complement of genes. How then can these cells
differentiate and form structures as different as roots,
stems, leaves, and fruits? The answer is that only a
(5) small subset of the genes in a particular kind of cell are
expressed, or turned on, at a given time. This is accom-
plished by a complex system of chemical messengers
that in plants include hormones and other regulatory
molecules. Five major hormones have been identified:
(10) auxin, abscisic acid, cytokinin, ethylene, and gibberel-
lin. Studies of plants have now identified a new class of
regulatory molecules called oligosaccharins.
Unlike the oligosaccharins, the five well-known plant
hormones are pleiotropic rather than specific, that is,
(15) each has more than one effect on the growth and devel-
opment of plants. The five has so many simultaneous
effects that they are not very useful in artificially
controlling the growth of crops. Auxin, for instance,
stimulates the rate of cell elongation, causes shoots to
(20) grow up and roots to grow down, and inhibits the
growth of lateral shoots. Auxin also causes the plant to
develop a vascular system, to form lateral roots, and to
produce ethylene.
The pleiotropy of the five well-studied plant
(25) hormones is somewhat analogous to that of certain
hormones in animal. For example, hormones from the
hypothalamus in the brain stimulate the anterior lobe
of the pituitary gland to synthesize and release many
different hormones, one of which stimulates the release
(30) of hormones from the adrenal cortex. These hormones
have specific effects on target organs all over the body.
One hormone stimulates the thyroid gland, for
example, another the ovarian follicle cells, and so forth.
In other words, there is a hierarchy of hormones.
(35) Such a hierarchy may also exist in plants. Oligosac-
charins are fragments of the cell wall released by
enzymes: different enzymes release different oligosac-
charins. There are indications that pleiotropic plant
hormones may actually function by activating the
(40) enzymes that release these other, more specific chemical
messengers from the cell wall.
作者解释了为什么所有的细胞在最初拥有相同基因的情况下，会生长成植物的各个不同部分。第一段，指出影响植物生长的成不同部分的是特定细胞中，在特定时间下的部分基因。整个相关系统含有化学信息：5种荷尔蒙，和OLIG.第二段，介绍了5种荷尔蒙的作用：每种都对植物产生多种影响。第三段，指出动物和植物一样：有与5种荷尔蒙作用类似的荷尔蒙，也有起特定作用的荷尔蒙。第四段，植物中起特定作用的物质：OLIG.产生过程：荷尔蒙刺激酶释放细胞壁，而OLIG是细胞壁上的片段，OLIG对植物起特定作用。
上面这些是我自己写的段意，不过对其中第3段的意思和作用不是很明确，按说文章就讲植物的，第1段提出两种东西，下面就应该分别讲这两个东西就OK吧？不知道这个动物这部分能起什么作用？不会是承上启下吧？？还有就是它的段意，看段的主题句（第1句）好象应该是要讲跟5种荷尔蒙类似的东西，可是没看明白它怎么就一下转到特别的荷尔蒙对动物起特定的作用的？？？
真的不明白 | 
