May 22, 19 1 3] 



NATURE 



299 



on the theatre wall at S. As only the figures them- 

 selves were seen, the rest of the screen must have 

 been dark, and therefore the background of each 

 picture must have been painted out on the film with 

 black (unless the film was unusually opaque). This 

 painting out would account for the absence of 

 the " rain " effect of the usual animatograph 

 reproduction. 



It is obvious from the foregoing that there is 

 no stereoscopic effect in the strict sense, i.e. that 

 there is no difference between the picture seen 

 by the right eye and that seen by the left eye, 

 at least so far as the figures are concerned. But 

 as the picture is a long way back on the stage 

 (some 40 ft. or more), so that the difference be- 

 tween the pictures that should be seen by the 

 two eyes would be quite small, and as the temple 

 itself is of course in relief, there is no difficulty 

 in imagining the figures to be in relief also ; in- 

 deed, as they step backwards and forwards the 

 illusion is very complete. 



Some parts of the glass were unfortunately 



■ n 1 

 



badly out of parallelism, and when the reflection 

 occurred at these places a doubling of the image 

 was produced, which made the figures very in- 

 distinct ; this, of course, cannot be avoided in such 

 a large sheet of glass. Some other defects that 

 we noticed could have been avoided. For instance, 

 the image of the edge of the screen PQ did not 

 quite coincide with the pillars CD ; so that when 

 the figures walked off the stage they disappeared 

 before they reached the pillars. Apparently the 

 image P'Q' is a little behind the plane CD (for this 

 defect was more evident at X than Z) ; if so, a 

 pair of pillars CD' should be so placed in front 

 of PQ as to form an image exactly coincident with 

 CD. Then, wherever the image was viewed from, 

 this parallax would disappear. We also noticed 

 that the barrel in one item, which was placed on 

 the stage, was not quite the shape or size of the 

 one in the picture. The upper part of a pillar at 

 B was rather brighter than the rest of the back- 

 ground, and could occasionally be seen through 

 the figures. It should be painted a little darker. 

 NO. 2273, VOL. 91] 



ERADICATION OF PLANT DISEASES. 

 THE general assembly of the International 

 -L Institute of Agriculture in session at Rome 

 has wisely refrained from extending the Phyllox- 

 era Convention to all cases of plant diseases. 

 Signor Cuboni's report on the diseases of plants 

 and the best method to prevent their propagation 

 gave rise to a lively discussion, but it was felt 

 that rough-and-ready measures would do more 

 harm than good. Ultimately a memorandum 

 was adopted conveying the following recommenda- 

 tions : — 



(1) The establishment of a Government service of 

 phytopathology by all Governments of countries adher- 

 ing to the International Institute of Agriculture. 



(2) The convening at an early date of an inter- 

 national conference of specialists with the view of arriv- 

 ing at an international agreement upon the means of 

 preventing plant diseases. The wish was expressed 

 that the French Government would follow up the 

 initiative it has already taken by calling such a meet- 

 ing. 



(3) At each general assembly of the institute the 

 specialists of the various Governments should meet in 

 a separate commission to discuss the results of their 

 researches and studies on the diseases of plants. 



(4) Countries adhering to the International Institute 

 should at once begin to study the various questions 

 which the International Commission of Phyto- 

 pathology will have before it, basing their study upon 

 the materials which the International Institute of 

 Agriculture will be able to furnish. 



The subject is one for concerted action. The 

 study of plant diseases is not a simple one. It 

 concerns the entomologist and protozoologist as 

 well as the botanist, and among botanists not 

 merely the students of fungi or bacteria, but the 

 physiologist and the investigator on Mendelian 

 lines ; for the production of disease-resisting forms 

 is one of the surest ways of eliminating the dis- 

 ease-factor. Furthermore, periodical meetings of 

 the workers in these various fields of investigation 

 will tend to encourage the worker, and will ensure 

 that the results of the work are put to the best 

 advantage. Comparison of results obtained in 

 the same line of research under the various con- 

 ditions offered by different countries will be speci- 

 ally helpful ; and if international legislation is to 

 follow, these various conditions must be carefully 

 considered. 



It should be obvious also that an organised 

 service of phytopathology is an essential, and an 

 ad hoc training of experts is a prime necessity. 

 The study of plant diseases offers ample scope 

 for investigation, and a Government service would 

 find work for a supply of experts at home and 

 abroad. One example will suffice. The Jamaica 

 banana industry has been recently threatened with 

 disaster because the Department of Agriculture 

 had no expert in plant diseases to recog- 

 nise on its outbreak a well-known disease which 

 had already caused serious loss to the same 

 industry in Central America. 



