188 NOTES AND COMMENTS [makch 



Professor Nawaschin points out that the condition in the elm is 

 transitional between the lower chalazoganiic and the assumedly higher 

 porogamic types. 



The ovary of Ulmus, in common with that of the typically 

 chalazoganiic forms, is devoid of the conducting tissue so characteristic 

 of those cases in which the nutrition of the pollen tube requires to be 

 provided for in its passage across the ovarian cavity. 



The ovule is of the pendulous inverted type, and in the great 

 majority of cases the pollen tube reaches it by growing down through 

 the tissue of the funicle not far from the surface till nearly opposite 

 the middle of the ovule when it strikes across through the integu- 

 ments, the outer of which is but slightly developed, to the apex of the 

 nucellus, thus avoiding alike micropyle and chalaza. In rare cases 

 the tube grows quite close to the surface of the funicle, in fact 

 among the epidermal cells, and even exhibits a tendency to project 

 into the surrounding cavity. These the author cites as indications of 

 a reaching out toward a higher porogamic life. On the other hand, 

 the tube sometimes enters the deeper tissues of the funicle and grows 

 directly towards the chalaza, where however it is stopped by a patch 

 of apparently cuticularised tissue. Here Professor Nawaschin sees a 

 reversion toward the ancestral chalazogamic condition typically repre- 

 sented in Casuarineae, Betulineae, and Jugiandeae. The extent to 

 which differences of this kind are to be treated as supplying a basis 

 for classification is at least a question open to discussion. 



A Theory of Colour Vision. 



Believing that the problem of colour vision is " primarily a mechanical 

 one," Dr. W. Patten, writing in the American Naturalist for November 

 1898, has given us a first instalment of an attempt to unravel the 

 mechanism. His brief notice of the Young-Helmholtz theory is 

 introduced by the words, " In Sir Isaac Newton's time there were 

 supposed to be three sets of fibres in the retina ! " Dr. Patten's 

 mechanical theory is based upon his claim to have found in the rods 

 of certain eyes — though not in those of the vertebrates — fine nerve 

 fibrils which traverse the rod always at right angles to the direction of 

 the light. As the light travels through the rods these fibrils are 

 stimulated in some way by the ether waves. In cones these fibrils 

 would naturally present regular diminishing scales, the longest at the 

 base, and the shortest at the tip ; the longest might, according to Dr. 

 Patten, be stimulated by the longer red waves, the shortest by the 

 violet waves. This is practically the whole theory, which rests upon 

 the gradual variation in the length of the transverse fibrils if they 

 could be shown to exist in cones. Passing over this stumbling-block, 



