648 THE POPULAR SCIENCE MONTHLY. 



force their way through the bark, penetrate the tissue, and take the 

 matter found there into their own systems. 



Still closer examination will reveal other features. In the first 

 place, there are none of the green leaves usually found on plants. 

 Secondly, there is no root fastening the plant to the soil. Why is this ? 

 What is the reason that this plant grows and flourishes like other 

 plants, and has yet neither root nor leaves ? Let us see. 



What is known as parasitism in plants is not confined to any one 

 family or class. Various orders have one or more genera with species 

 which take their nourishment in a complete or partly elaborated form 

 from other plants. Sometimes they are perfect parasites, and take 

 everything they need from other vegetable forms. Sometimes, as in 

 the mistletoe, they take the partially made sap, and complete its trans- 

 formation within their own tissue ; while in still other instances only 

 a very little of the sap is taken, and the other nourishment is absorbed 

 from the soil by the roots proper. 



Our dodder is an example of a perfect parasite. All the material 

 necessary for its growth it takes ready made from the plants upon 

 which it grows. As the purpose of leaves in all plants is to prepare 

 from the crude materials in the air and soil the matter necessary for 

 its growth, and as the dodder finds and appropriates this material 

 already made, the absence of leaves is at once accounted for. There 

 was no need for them, and they ceased to be. 



The want of a root is another matter. When the seed of the dod- 

 der is examined, it is found that there is simply a coiled embryo, with 

 very little albumen. The usual seed-leaves are absent ; so that, for 

 its first growth, it must depend entirely iipon the albumen in the seed. 

 When this seed first germinates, a little rootlet penetrates the ground. 

 Owing to the deficiency of food, it only exists long enough to enable 

 its stem to grow till it reaches some plant upon which it can fasten. 

 When this is accomplished, the young plant will grow rapidly, and 

 soon sever its connection with the ground ; but, if not able to reach 

 some support, it dies entirely. 



In order to comprehend the reasons for the peculiarities of the dod- 

 der, and understand how it came to assume its habit of complete para- 

 sitism, it will be necessary to notice the probable rise and progress of 

 the habit. We can do this by looking at some of those plants which 

 are not yet such complete pensioners on the bounty of others. For it 

 very seldom happens that all the steps leading from a normal to an 

 out-of-the-way mode of living ai-e lost. Some few will remain, to in- 

 dicate the line along which the plant has proceeded. Imperfect adap- 

 tations point surely the path leading to perfect development. 



The modes of living of the dodder and the Indian pipe may be con- 

 sidered as the two extremes of one line of development. The first is 

 a complete parasite, and the second has gone so far as to become a 

 saprophyte. The central point from which sprang the two branches 



