368 



Minnesota Plant Life. 



flowers about two inches long. The other variety has ovate, 

 bkint-pointed leaves, often very large and somewhat heart- 

 shaped at the base. The form with the arrow-head-shaped 

 leaves is much more common and is found trailing over shrub- 

 berv in thickets or in the edges of woods. 



Dodders. Dodders are very curious parasitic plants, closely 

 related to the morning-glories. They may be considered as 

 twining morning-glories which have acquired the habit of suck- 

 ing up their food 

 from the bodies 

 of the plants 

 upon which they 

 climb. As a 

 consequence of 

 this habit their 

 leaves have been 

 reduced to tiny 

 scales, being no 

 more employed 

 in starch-mak- 

 ing, and their 

 stems, no longer 

 green, have be- 

 come yellow or 

 white in color. 

 Dodder often 

 produces great 

 intricate tangles 

 of threads, like 

 so much yellow 

 yarn, looping over the herbs or shrubs from the tissues of which 

 they extract their nutriment. Another variety of dodder that 

 o-rows on the stems of sunflowers, goldenrods and asters, looks 

 like three or four turns of rope around the axis of the host plant. 

 The relationship of the dodders to the morning-glories may 

 be seen in their capsules and seeds which strongly bring to 

 mind tlic well-known ])ods of the ordinary cultivated morn- 

 ing-glorv. In Minnesota the following varieties of dodder mav 

 be distinguished: The field dodder, with sepals of the calyx 



Fig. 17.5. Dodder in flower; the parasite is seen to be clutching 

 tightly the stem of its host plant. After Atkinson. 



