194 SUMMARY OF CURRENT RESEARCHES RELATING TO 



BOTANY. 



GENERAL, 

 Including the Anatomy and Physiology of Seed Plants. 



Structure and Development. 



Vegetative. 



Morphology of Ceratozamia.* — C. J. Chamberlain describes the 

 morphology of this interesting Mexican Cycad. From observations in 

 its wild habitat lie finds that it grows best in well shaded mesophytic 

 conditions. The plant in passing from the seedling to the adult stage 

 shows a progressive change in its leaves, the leaflets becoming larger, 

 broader, thicker, and more numerous : the ovuliferous cone also shows 

 considerable variation in the size and number of its sporophylls. In 

 addition to the primary haustorium, a system of secondary haustoria is 

 developed later from the basal portions of the polleu-tube. There are 

 regularly two sperms, but occasionally four are produced. A small 

 ventral canal nucleus is present which occasionally enlarges and may 

 fertilize the egg ; this may explain the so-called hybrids obtained by 

 Van Tieghem. In most cases fertilization occurs in the normal way. 

 Both the suspensors and the young embryos may unite so that from five 

 fertilized eggs there may develop one to five embryos. The mature seed 

 contains one embryo with a single cotyledon. 



Reproductive. 



Paired Leaf-formations.| — K. Goebel has studied the relative posi- 

 tions of stamens and perianth in a large number of species, and is of the 

 opinion that Cordemoy is wrong in his views as to the order of growth 

 of the different parts of the flower, i.e. first outer perianth, second inner 

 perianth, third outer stamens, etc. Many examples are quoted as being 

 contrary to this arrangement. Thus, in Triglochin maritimum each 

 stamen follows the appearance of the perianth-segment to which it is 

 opposite, and the outer stamens arise at the same level as the inner 

 perianth-leaves. In Scheuchzeria palustris the conditions indicate a 

 "pairing" of perianth-leaves and stamens, i.e. the same relative posi- 

 tions as with buds growing in the axils of leaves. In Potamogoton the 

 author agrees with Hegelmaier in regarding the perianth and stamens as 

 independent structures, and also finds indications of " pairing." Ruppia 

 is not to be regarded as primitive and therefore its structure cannot be 

 compared with Potamogeton, as is usually done. Instances of " pairing " 

 are common among the Dicotyledons, as shown by various species of 

 Alnus, and several of the Urticacea3 and Loranthacese, and in Viscum 

 the condition is so extreme that the stamens have entirely lost their 

 independence and arise out of the perianth-segments. 



* Bot. Gaz.. lii. (1912) pp. 1-19 (1 pL). 

 t Flora, iii. (1911) pp. 248-62 (9 figs.). 



