CLIMBING PARASITES. GREEN-LEAVED PARASITES. TOOTHWORT. 171 



however, to mention the fact that the various species of Chytridese and Sapro- 

 legniacese do not content themselves with plants that are second-rate hosts, but 

 exercise a selection amongst the different green algae living in the water. It is 

 astonishing to find that the swarm-spores invariably swim to cells whose protoplasm 

 affords the most suitable nutrient basis for them, and attach themselves to those 

 cells only, and never on other species unadapted to their requirements. 



CLIMBING PAEASITES. GEEEN-LEAVED PARASITES. TOOTHWORT. 



The third group into which parasites were divided at the beginning of this 

 chapter is composed of flowering plants throughout. According to their method of 

 attacking the host for the purpose of absorbing nutriment from it, they range 

 themselves in six series. In the following pages we shall discuss the charac- 

 teristics of each series as manifested in the most remarkable forms belonging 

 to it. 



The first series includes plants destitute of green leaves and of chlorophyll in 

 general, whose seeds germinate on the ground and send forth each a filiform stem, 

 which brings itself, by means of peculiar movements, into contact with the host- 

 plant, coils round it, and develops organs of suction whereby it takes nutriment 

 from the plant assailed. 



To this series belong the genera Cassytha and Cuscuta. The former includes 

 some thirty species, all of which appertain to warm climates. Most of the Cass}^- 

 thae inhabit Australia, where they attack, in particular, the copses of Casuarinae 

 and Melaleucse, fastening their wart-shaped, or, in many cases, shield-like or discoid 

 suckers upon the young green shoots of those plants. Several species also are 

 indigenous to New Zealand, others to Borneo, Java, Ceylon, the Philippines, and 

 the Moluccas. South Africa, too, is the home of a few Cassythae, and one species 

 (C. Americana) is distributed over the West Indies, Mexico, and Brazil. A 

 European, seeing these parasites with their twining, thread-like, leafless stems, and 

 their flowers aggregated in capitula, umbels, or spikes, takes them at first to be 

 species of the genus Cuscuta, popularly called Dodder. That these plants should 

 be most nearly related to laurel-trees is the last thing one would expect. Ex- 

 amination of the flowers and fruit reveals, it is true, a close resemblance to those of 

 laurel and cinnamon trees, and, therefore, these Cassythae are rightly placed by 

 systematic botanists among the Lauraceae. But in respect of food-absorption, as in 

 general aspect, they are entirely analogous to the various species of the genus 

 Cuscuta, which belong to the family of Bindweeds (Convolvulacese). The last- 

 named genus is even more variously differentiated than the genus Cassytha, and 

 includes about fifty species dispersed pretty evenly over the whole world. Every 

 part of the world has its own characteristic forms. One group occurs in California, 

 Carolina, Indiana, Missouri, and Mexico, another in the W T est Indies, Brazil, Peru, and 

 Chili, a third at the Cape of Good Hope. Other species are natives of China, the 

 East Indies, the steppes of Central Asia, Persia, Syria, the Caucasus, and Egypt. 



