370 SUMMARY OF CURRENT RESEARCHES RELATING TO 



middle of each day on Egypt, the number of these layers corresponded 

 to the number of nights during which the growth in thickness of the 

 cell-wall had continued. These concentric layers in the wall of Egyptian 

 cotton hairs are thus rings of nightly growth, differentiated by hetero- 

 geneity like the annual rings in timber. These rings are coarser, more 

 sharply demarcated and less regular in fuzz hairs than in lint hairs. The 

 later rings in fuzz hairs may resemble those of lint hairs. Certain 

 abnormal appearances indicate that the cellulose wall may grow for 

 a time without being in full contact with the ectoplasm. J. E. 



Reproductive. 



Fruit of Opuntia. — D. S. Johnson {Puh. Carneg. Inst. Washington, 

 1918, 1-62, 12 pis.). The author has studied 0. fulgida with special 

 reference to the perennation and proliferation of the fniits. Fruits of 

 some Opuntias are known to remain attached to the plant and to grow 

 actively for several years; in 0. fulgida this condition is carried still 

 farther, for not only does the fruit remain on the tree without shedding 

 its seed, but both the ripe fruit and the unripe ovary may give rise to 

 flowers and another crop of fruits. Four or five generations of fruits 

 may thus be formed on a tree during one season. Also, when a ripe 

 fruit falls to the ground, it may put out adventitious roots and shoots 

 and so produce a new plant. The fleshy joints of this plant readily 

 break off, sprout and form new plants strongly resembling those resulting 

 from the vegetative development of the ovary ; moreover, such joints 

 become very much like a flower in appearance. Comparison of such a 

 joint with the final development of the outer wall of the ovary and 

 fruit, both from the morphological and physiological aspect, leads to the 

 conclusion that the flower of this Opuntia has been evolved from one 

 with a superior ovary, through progressive submergence of the ovary by 

 stronger growth of the parts of the fertile joint. This flower is 

 probably a primitive type among the Cactaceas, from which the type 

 found in Cereus and Echinocactus has been derived. 



The number of well-matured seeds in a single fruit varies from to 

 100, or even 200. Each seed contains a large coiled embryo and a 

 small amount of endosperm, and may remain for several years in the 

 fruit without losing the power of germination, and there appears to be 

 reason for believing that the fruit-pulp inhibits germination. When 

 the fruits fall on moist ground they produce adventitious roots and 

 vegetative shoots, thus giving rise to new plants independently of the 

 seed. This method of reproduction, together with the proliferation of 

 detached joints, forms the chief means of multiplication and dispersal of 

 this cactus. Similar cases of persistence and proliferation of the fruit 

 are not unknown in other species. In 0. versicolor and other flat- 

 jointed Opuntias, this is due to the cactus-fly laying its eggs in the fruit, 

 but at present nothing is known as to the cause in 0. fulgida. S. G-. 



Embryogeny of Capsella. — R. Soueges {Ann. Sci. Nat. Botan. 

 Paris, 1919, Ser. 10, 1, 1-28, 69 figs.). The author has studied the 

 development of the embryo in Capsella Bursa-Fastoris, with special 



