就是虚拟语气.意思是这个植物已经死了,我早都应该给它浇水了!（实际上他没有浇啊,所以就用虚拟语气）
省略if的倒装句
虚拟语气的非真实条件句中若含有“were,had,should等词”,可以省略连词if,并把were等移到句首,构成倒装.
Were he here now,he would tell us what to do.
如果他现在有在这儿,他会告诉我们该作些什么.（事实上他不在这儿.）
Had I the time,I would go.
如有时间我就去.
Should it not rain,the crops would die.
要是不下雨,庄稼就要死了.
Had I read the paper yesterday,I should have known about his death.
假如我昨天看了报纸的话,就会知道他的死讯.
Should he refuse to leave,call me at the office.
万一他拒绝离开,你就给我打电话到办公室来.