1 40 



NATURE 



[April 10, 191, 



believes that the post-flagellate phase finds 

 its way back again to the human being, 

 when the bug feeds again, by regurgitation from the 

 intestine. Proof of this is as yet lacking, but he hopes 

 in future experiments to solve this part of the problem 

 once and for all. He states that if the bug takes a 

 fresh feed of blood when the parasites in its intestine 

 are in the flagellated phase, they are all destroyed, 

 and cannot develop further. " Human blood has some 

 body in it which not only prevents the process of 

 flagellation, but also destroys the flagellates. This 

 substance is in all probability the complement, and it 

 is known that it is itself destroyed in about two days, 

 when blood is drawn from the human body. This fact 

 further explains why the parasite only begins its 

 development in the bug on the second day. . . . 

 Though many bugs may become infected, only those 

 which do not feed again till the parasite has passed 

 back to its post-flagellate stage are infective." He 

 believes that only in its "post-flagellate" leishmanial 

 form can the parasite resist the destructive action of 

 fresh blood and re-infect the vertebrate host. 



The author's conclusion that a non-flagellate leish- 

 manial stage is the final phase in the development of 

 the parasite in the insect-host is based largely on a 

 comparison with the herpetomonad parasites of in- 

 sects ; that is to say, on an analogy with species which 

 are parasitic in invertebrate hosts alone and have no 

 alternate vertebrate host in their life-cycle. In such 

 species, however, the infection of new hosts is effected 

 (apart from the possible occurrence of " hereditary " 

 infection) bv the contaminative method; that is to say, 

 by means of resting, non-flagellate phases, usually 

 encysted, which pass out of the host in the fasces, and 

 are accidentally swallowed by another insect-host. On 

 the other hand, in all known cases where a flagellate 

 parasite has an alternation of hosts, vertebrate and 

 invertebrate, and where the vertebrate host is infected 

 by the inoculative method, that is to say, by the 

 parasite being injected into it through the mouth- 

 parts of the invertebrate in the act of sucking blood ; 

 in all such cases that have been investigated accurately 

 up to the present, the final stage of the parasite in 

 the invertebrate host is an active flagellate. Further, 

 it has been frequently observed in, for instance, the 

 development of trypanosomes in their alternate in- 

 vertebrate hosts that the active, flagellate forms, 

 usually crithidial or herpetomonad in type, may pass 

 temporarily into a resting, non-flagellate, leishmanial 

 phase during hunger-periods, when the ingested blood 

 is digested and absorbed, and become active flagellate 

 forms again when the host takes in a fresh supply of 

 food. 



From these considerations the possibility is not to 

 be excluded at present that Captain Patton's observa- 

 tions mav be capable of an interpretation different from 

 that which he places upon thern. It may well be that 

 his "post-flagellate" stage represents a resting phase 

 upon which the parasite enters when the blood taken 

 up by the bug is digested, and that when the bug 

 feeds again these resting forms will become active 

 once more, and give rise to a final flagellate stage, yet 

 to be discovered, which will be inoculated ultimately 

 into the human being. It must, however, be borne 

 in mind that it has not yet been proved definitely that 

 the parasite passes from the bug into the human 

 being by inoculation through the proboscis; if, as is at 

 least possible, the parasite is destined to pass out of 

 the bug in its faeces, it is then probable in the highest 

 degree that the final stage in the development in the 

 buc would be a resting, non-flagellate phase. 



The final decision, however, with regard to the 

 transmission of the parasite of Kala-azar will rest, 

 not upon analogies with other parasites, but upon facts 



NO. 2267, VOL. 91] 



demonstrated with regard to this parasite itself, and 

 if Captain Patton establishes his statements, he will 

 have added a new type of development and trans- 

 mission to those known already to occur in flagellate 

 parasites of vertebrates transmitted by blood-sucking 

 invertebrates. However this may be, the author is 

 to be congratulated on having brought forward very 

 strong evidence to show that, as suggested originally 

 by Rogers, the spread of this very deadly human 

 disease is to be attributed to the agency of the bed- 

 bug, a discovery of immense practical importance. 



E. A. MlNCHIN. 



NEW ZEALAND VEGETATIONS 

 I N a brief general account, contributed to the " New 

 *■ Zealand Year-book, 1912," Dr. L. Cockayne, 

 F.R.S., who has done so much floristic and ecological 

 work in New Zealand, points out that owing to its 

 long isolation and diverse elements (Malayan, Aus- 

 tralian, subantarctie, and endemic), the flora of New 

 Zealand is of special interest. 



The vascular plants in this flora — ferns, fern-allies, 

 and seed-plants — number, so far as at present known, 

 about 1700 species, of which about three-fourths are 

 endemic. Of the lower plants — algse, fungi, lichens, 

 liverworts, and mosses — many hundreds have been 

 described, including many remarkable genera and 

 species, but there can be no doubt that hundreds 

 more remain to be described. The ferns and fern- 

 allies form a striking feature in the vegetation in 

 some areas, but are not of such great relative import- 

 ance in the New Zealand flora as has sometimes been 

 supposed ; still, about 160 species of these plants are 

 known. 



Among the seed-plants, the daisy family is the 

 largest, as might be expected, having more than 230 

 species; the sedge, grass, and figwort families follow 

 with more than 100 species each, while between thirty 

 and seventy species belong in each case to the orchid, 

 carrot, buttercup, bedstraw, epacrid, willowherb, pea, 

 rush, and forget-me-not families. 



Among genera which contain many species and are 

 marked by great variability, making them difficult 

 to define and classify, Dr. Cockayne mentions 

 Veronica, Carex, Ranunculus, Senecio, Epilobium, 

 and Myosotis. The genus Veronica, with more than 

 100 species, is remarkable for its variability and for 

 the almost endless variety of habit assumed by the 

 various species, some of the New Zealand speedwells 

 (mostly endemic and largely alpine in habitat) being 

 small trees, while the majority are shrubby and often 

 dwarf, frequently simulating cypresses and other 

 conifers owing to their reduced and appressed leaves. 

 Apart from variability in the adult plants, about 100 

 New Zealand species, belonging to different genera, 

 have juvenile forms which are quite distinct from the 

 adult forms, and may retain their juvenile characters 

 for many years; this is seen in various trees, such as 

 lace-bark, lancewood, and ribbonwood. 



Among the multitudinous growth-forms, character- 

 istic of diverse life conditions, the more remarkable 

 are the climbers with woody rope-like stems, re- 

 sembling the lianas of the South American tropical 

 forests ; shrubs with wiry interlaced branches forming 

 close masses ; the curious cushion-plants, sometimes of 

 immense size, as in the vegetable sheep (species of 

 Haastia, Raoulia, and Psychrophyton) ; leafless shrubs 

 with round or flattened stems, and so on. The woodv 

 plants are almost all evergreen, onlv some twentv 

 species being deciduous or semi-deciduous; herbs that 



1 The Flora of New Zealand." By Dr. L. Cockayne. Extract from 

 the " New Zealand Year-boi 1 



