64 SUMMARY OF CURRENT RESEARCHES RELATING TO 



fat. but there is no evidence to show that this has any direct connexion 

 with the pigment. The latter appears in three forms : {a) diffuse and 

 composed of indistinct granules, (b) distinctly granular, (c) crystalline. 

 All the observations tend to prove that the plastids are a variety of 

 mitochondrias which are differentiated at a very early stage and adapted 

 to a special function. With very few exceptions the pigments are 

 formed directly and without any previous formation of chlorophyll. 

 Pigment-formation in plants resembles that recently noticed in certain 

 animal-cells. S. Greves. 



Microsporog-enesis in Datura. — C. E. O'Neal (Bull Torr. Bot. Club, 

 1920, 47, 2;!1-4:1, 2 pis.). The author has studied the cytology of 

 Datura Stramonium, with special reference to the Mendelian theory. The 

 writer contirms Bonicke's statement that this species has twelve bivalent 

 chromosomes, and finds that the parts of the latter which are cut from 

 the spireme thread form twisted loops or rings, or less often assume a 

 U-shape ; from this time until the telophose of the second division they 

 do not lose their individuality. The most striking feature of these 

 chromosomes is their remarkable uniformity of size, luit no basis can be 

 found for any Mendelian characters which would result in the occurrence 

 of mutants. The exact results obtained by breeders appear to be due to 

 unusual regularity in the formation and behaviour of the chromosomes. 



S. G. 



Statocytes of Wheat.— T. L. Prankerd {Bot. Gaz., 1920, 70, 

 148-52, i tigs.). The statocytes of the wheat-haulm are of two types 

 — smaller ones containing movable starch-grains, and larger ones con- 

 taining a single movable crystal of calcium oxalate ; both types are 

 found at the nodes. The rate of fall of the crystal in the largest type 

 is much greater, and the period of migration less than in the case of 

 those statocytes containing starch -grains. The author suggests that the 

 nodes of wheat should be regarded as sense-organs of a high degree of 

 evolution, and that in all future studies as to the reaction of the plant to 

 gravity this point of view should be considered. S. G. 



Structure and Development. 

 Vegetative. 



Stem- anatomy of Dioon. — L. M. Langdon {Bot. Gaz., 1920, 70, 

 110-25, 3 pis., 4 figs.). In the stem of Dioon spi7wJosum iheve are three 

 types of medullary rays : (1) uniseriate rays, which are one cell in width 

 and several cells deep ; (2) multiseriate rays, which are two or more 

 cells wide and of variable depth ; (3) broad foliar rays or leaf-gaps. 

 The fibro-vascular elements of the latter, together with those of tlieir 

 connexions with the secondary wood, have peculiar, irregular, scalari- 

 form tracheids, which curve down until they become inserted in the 

 fibrous elements of the main stele. The regular pitted vessels are 

 diverted sideways parallel to the leaf-trace. Both the scalariform and 

 pitted vessels exhibit a marked sliding growth. Each leaf or leaf-scale 

 has seven to nine strands, the two inner of which take a direct vertical 



