1. poem的意思是“诗”，为可数名词，可指具体的一首诗、两首诗、几首诗等;用作主语时，谓语动词的数取决于poem的数(即poem为单数，谓语动词用单数;poem为复数，谓语动词用复数)。如：

This poem is worth learning by heart. 这首诗是值得记起来的。

His poems have been compared to those of the English Romantics. 他的诗歌被拿来与英国浪漫主义诗歌相提并论。

2. poetry的意思也是“诗”，但为诗的总称，是不可数名词;用作主语时，谓语动词总是用单数。如：

This writer’s poetry reflects his love of nature. 该作者的诗反映出他热爱自然。

Poetry has been composed since ancient times. 从古时起人们就开始创作诗歌了。

Poetry serves to stimulate the mind. 诗歌能激发心灵。