POLLINATION AND FERTILIZATION 



147 



Npad 



spathe 



numbers of gnats or midges are attracted to the flower cluster 

 and do not easily find their way out of the chamber in which 

 it is inclosed, but when they do escape, carry pollen with them 

 to the next jack-in-the-pulpit which they visit, and pollinate 

 the flowers there. 



The flower cluster 

 of the common Euro- 

 pean arum 1 has been 

 so much more carefully 

 studied than that of 

 our related American 

 plant, and is so much 

 more successful in de- 

 taining pollinating in- 

 sects, that it is worth 

 while to describe it in 

 some detail. The cham- 

 ber which surrounds FIG. 132. Pitfall flower clusters of the 

 the flower cluster ap- European arum 



pears to be moderately 

 open, and admits the 

 free entrance and exit 

 of small insects. The 

 spadix, or floral axis, 

 bears several rows 

 of downward-pointing 

 bristles (fig. 132, B}. 

 Small midges are at- 

 tracted to the interior of the flower chamber by its peculiar 

 ammonia-like smell and by its warmth, which is considerably 

 greater than that of the outside air. The midges readily 

 crawl down through the palisade hairs, often bringing with 

 them pollen with which they have become dusted in other 

 arum-flower clusters. As they crawl down the spadix they 

 pass over the immature staminate flowers (fig. 132, ) and 

 1 Arum maculatum. 



A, exterior view of the flower cluster, about one 

 third natural size ; B, the same drawn to a larger 

 scale, with part of the covering removed ; C, part 

 of B, drawn to still larger scale, with the flowers 

 more mature and the hairs (h) withering and al- 

 lowing the escape of imprisoned midges; spad, 

 spadix, or floral axis; spathe, the hood covering 

 the axis ; h, hairs closing narrowed part of spathe ; 

 stam, group of staminate flowers (not mature in 



B, mature in C) ; pist, group of pistillate flowers 

 (just matured in B, pollinated and developing 



seeds in C). A and B, after H. Miiller 



