DEVELOPMENT OF PLANTS 413 



being perfect, and in addition containing a perianth of four 

 sepals which arch over the sporophylls. The crossing of the 

 flowers is effected in a variety of ways. In some cases the in- 

 conspicuous stigmas first push out from between the sepals so 

 that microspores must be brought from another earlier flowering 

 plant. In other cases, the stamens at the top of the spadix are 

 first extruded and shed their spores; while at the bottom of the 

 spadix the reverse condition obtains, the stigmas being in a re- 

 ceptive condition. This might result in a crossing of the upper 

 flowers with the lower, and later, when the lower flowers put 

 out their stamens and the upper their stigmas, insects could effect 

 a reverse crossing. As the seeds mature the spadix and sepals 

 become large and spongy, enclosing the ovaries which are finally 

 set free by the decay of the spadix, as fleshy berries. This fruit 

 is admirably adapted to the aquatic habit of these plants and 

 readily floats in the water, owing to the spongy outer tissues, and 

 so bring about the distribution of the seeds. The jack-in-the- 

 pulpit has a surer method for effecting a crossing, since the 

 sporophylls are usually borne on separate spadices. You will 

 often find, however, spadices with a few stamens situated just 

 above the pistillate flowers. The flowers are very simple, con- 

 sisting of a single naked pistil or of four nearly sessile stamens 

 (Fig. 286, C-D). The fruit is a shining bright red berry. 



In some of the tropical genera the insects are held in the 

 spathe by hairs that extend obliquely downwards, thus permit- 

 ting the entrance but blocking the exit of the insects until cross- 

 ing of the flowers has been effected. In one of the species of 

 Arum there are two sets of hairs that divide the spathe into two 

 compartments containing respectively staminate and pistillate 

 flowers (Fig. 286, ). As soon as the spathe opens the insect 

 ladened with microspores from another flower makes his way to 

 the lower chamber, where the stigmas are in a receptive condi- 

 tion. Here he is held a prisoner and rubs the microspores upon 

 the stigmas as he wanders about in the compartment. When the 

 microspores in the upper chamber begin to discharge, the lower 

 set of hairs wither, giving him entrance to this chamber, where 

 he feeds upon the microspores and becomes covered with them. 



