190 



BOTANY 



PART I 



lating plants, the amount of chlorophyll present is in reality so small that it is 

 evident that Cuscuta (Dodder) affords an example of a very complete parasite. 



The embryonic Ouscula plantlet, coiled up in the seeds, pushes up from the 

 ground in the spring, but even then it makes no use of its cotyledons as a means 

 of nourishment ; they always remain in an undeveloped condition (Fig. 221 at the 

 right). Nor does any underground root-system develop from the young rootlet, 



PIG. 221. Cuscuta europaea. On the right, germinating seedlings. .In the middle, a plant of 

 Cuscuta parasitic on a Willow- twig ; b, reduced leaves ; Bl, flower-clusters. On the left, cross- 

 section of the host plant W, showing haustoria H of the parasite Cus, penetrating the cortical 

 parenchyma and in intimate contact with the xylem v and the phloem c of the vascular 

 bundles ; s, displaced cap of sheathing sclerenchyma. (After NOLL.) 



which soon dies off. The seedling becomes at once drawn out into a long 

 thin filament, the free end of which moves in wide circles, and so inevitably 

 discovers any plant, available as a host, that may be growing within its reach. 

 In case its search for a host plant is unsuccessful, the seedling is still able to creep 

 a short distance farther at the expense of the nourishing matter drawn from the 

 other extremity of the filament, which then dies off (t) as the growing extremity 

 lengthens. If the free end, in the course of its circling movements, comes 



