74 Flowers and their Unbidden' Guests, 



•which would be 4 mm. above them ; and thus the 

 nectar would be expended without profit to the plant, 

 Such access, however, to the flower from below is 

 rendered impossible to all small insects, wiaged and 

 wingless alike, by the above-described formation of the 

 involucrum. Supposing a small winged insect to have 

 crept up the stem as far as this involucrum, and still 

 to aspire after the nectar, there is no other course open 

 to it than to take to its wings, pass over the obstacle 

 by flight, and thus approach the flower from above, 

 that is, by the path which will inevitably bring it into 

 contact with the stigma. Thus the prickly scales of 

 the involucrum protect the flowers, or rather the nectar 

 which the flowers secrete, only in the sense that they 

 prevent the nectar being got at from below. It is only 

 when visitors would make their approach in this direc- 

 tion, that they are unwelcome. Let them come from 

 any other side, and their visits are in the highest degree 

 acceptable. Protective appliances of this character — 

 to which we may not unfitly give the name of " path- 

 pointers" — are of extraordinary frequency, and amongst 

 them are to be reckoned numerous prickly formations 

 occurring in the neighbourhood of the flowers. 



It has already been stated that the prickles and 

 sharp bristles which beset the epiderm of the axis, as 

 also the needle-Kke processes of the lower bracts, 

 usually point downwards ; the object manifestly being 

 to keep off such soft-skinned animals as would creep up 



