The reply, coming with less than his customary delay, took his favourite form of counter-interrogation:

'With what does a plant think -- in the absence of a brain?'

'Ah, plants also belong to the philosopher class! I should be pleased to know some of their conclusions; you may omit the premises¹.'

'Perhaps,' he replied, apparently² unaffected by my foolish irony³（讽刺，反语） , 'you may be able to infer their convictions from their acts. I will spare you the familiar examples of the sensitive mimosa（含羞草） , the several insectivorous（食虫的） flowers and those whose stamens（雄蕊） bend down and shake their pollen⁴ upon the entering bee in order that he may fertilize⁵ their distant mates. But observe this. In an open spot in my garden I planted a climbing vine. When it was barely above the surface I set a stake into the soil a yard away. The vine at once made for it, but as it was about to reach it after several days I removed it a few feet. The vine at once altered its course, making an acute angle, and again made for the stake. This manoeuvre⁶（策略） was repeated several times, but finally, as if discouraged, the vine abandoned the pursuit and ignoring further attempts to divert it, travelled to a small tree, farther away, which it climbed.

'Roots of the eucalyptus⁷（桉树） will prolong themselves incredibly in search of moisture. A well-known horticulturist（园艺家） relates that one entered an old drain-pipe and followed it until it came to a break, where a section of the pipe had been removed to make way for a stone wall that had been built across its course. The root left the drain and followed the wall until it found an opening where a stone had fallen out. It crept through and following the other side of the wall back to the drain, entered the unexplored part and resumed its journey.'

'And all this?'

'Can you miss the significance of it? It shows the consciousness of plants. It proves that they think.'

'Even if it did -- what then? We were speaking, not of plants, but of machines. They may be composed partly of wood -- wood that has no longer vitality⁸ -- or wholly of metal. Is thought an attribute also of the mineral kingdom?'

'How else do you explain the phenomena⁹, for example, of crystallization?'