SELF-FERTILISED FLOWERS 181 



Now, from this humblest of flowering plants we 

 may deduce two facts: first, self-fertilisation has 

 been so successful that the duck-weed survives, and 

 has spread out all over the world ; second, the plant 

 has not been able to develop and raise itself to a 

 higher form of life. 



F. Ludwig expresses the opinion that duckweed 

 is adapted for fertilisation by insects which live on 

 the water, and undoubtedly there is no barrier to 

 prevent it. In fact, insects may occasionally have 

 crossed the pollen of some plants long ago, thus 

 causing slight variations which are classified in four 

 distinct species. In spite of this, however, the duck- 

 weed stands as an example of what self-fertilisation 

 can and cannot accomplish. 



So far as we know there is but one plant or 

 flower which is self -fertilised by an insect: namely, 

 the Spanish bayonet-^a native of JNIexico but 

 acclimatised in our Northern States. 



Spanish Bayonet — Yucca 

 June-July 



This is a very handsome and decorative plant, 

 familiar in our gardens. From a thick cluster of 

 stiff", divergent leaves, each armed with a cruelly 

 sharp point, rises a flower-spike three to five feet 

 tall, covered with ivory-white blossoms resembling 



