318 TWENTY-FIRST REPORT. 



ill the host. The presence of abundant well-developed chloroplasts insures a 

 supply of its own organic food. But yot it seems likely that something else 

 may ho obtained frojn the host, for it has been noted that only those zygotes 

 <-i»ntiiino their devolopniont that have the fortune to find and enter the host 

 plant. Among the Rhodophyeeao, many genera are almost entirely end<tphytic 

 witliin other Red Seaweeds, without losing their colored chloroplasts. P.ut 

 wo note that they only occur in such habitats, a suspicious sign, and further- 

 more their vegetative development is almost exclusively of the simpler filamen- 

 tous tj'pe, indicating perhaps that the semi-parasitic habit had at least not 

 been favorable to the development of a more complicated or massive type of 

 vegetative structure, such as is often found in their very near relatives. 



I'erhaps almost on a par with these are those Anthophyta that still possess 

 well-developed green leaves, but which are undoubtedly at least partial pai-a- 

 sites, sudi as some species of Mistletoes (Viscum or Phoradendron) and plants 

 like Comandra, etc. These have undoubtedly the power to produce part, if 

 not most, of their organic food in their own leaves, yet their growth and 

 development are dependent upon their direct physical attachment to the proper 

 host. Already the simple leaves of medium size or even small and the paler 

 green color proclaim their fall from grace. 



Apparently, however, endophytism, partial or complete, is the fatal step, 

 for we find many plants that in other characters are closely allied to those 

 just mentioned which have gone to the next logical step and have lost h\l of 

 their own power to manufacture their organic food. Thus closely related to 

 ( -hlorochytrium, we find Rhodochytrium, an endophytic alga in the United 

 States in the tissues of Ambrosia. This plant lias no chlorophyll, although 

 it still seems to possess rudimentary plastids containing a red coloring matter, 

 probably one of the carotins. Beyond a somewhat marked tendency toward 

 the elongation of the plant Ixidy whereby it is able to reach more host cells, 

 and the loss of the chlorophyll and reduction in size of the plastids, the modifi- 

 cations as yet are not very great. A step further and we find Synchtyrium. 

 Here even the rudimentary plastid is gone, and with it the last remnant of 

 the carotin. These plants are obligate parasites, now intracellular, not mei'ely 

 intercellular. With the simple plant body to liegiu with, the steps downward 

 to complete pai-asitism have brought few modificati<ms. With more complex 

 structures, however, we find that this is not the case. 



The endophytic Rhodophyceae have been mentioned above. They were 

 rather simply branched filaments with red chloroplasts containing in addition 

 to chlorophyll and the carotin-like compounds, a violet red coloring matter 

 phycoerythrin. A few species are known that are complete parasites. Among 

 these Harvcyclla mirahilis is, as its name denotes, a very notable one. It 

 consists of much branching filaments of short, slender,' colorless cells which 

 force their way between the cells of the host (also one of the Red Seaweeds) 

 in exactly the manner of a fungus. The host cells are sometimes forced entirely 



