June 23, ie05.] 



SCIENCE. 



951 



the fruit, even the dead pollen serving to 

 call forth this response. Under such cir- 

 cumstances it may well be that other chem- 

 ical stimuli may produce the same effect. 

 On the whole, there are no more interesting 

 problems in physiology than those relating 

 to pollination, the penetration of the pollen 

 tube, and conditions of fertilization. ]\Iany 

 phases of these problems have thus far been 

 studied by gardeners and horticulturists 

 alone. 



In this connection may be mentioned 

 another fusion phenomenon of physiolog- 

 ical interest — that of double fertilization in 

 the angiosperms. This fusion of the sec- 

 ond sperm nucleus with the endosperm 

 nucleus (itself a compound of two nuclei 

 of the gametic groups) or with one of the 

 polar nuclei, may have a special signifi- 

 cance, or it may be merely the expression 

 of the fusion tendency which has not been 

 lost, although the function of the endo- 

 sperm nucleus may have undergone spe- 

 cialization. In the case of the pine, it will 

 be remembered that the second sperm 

 nucleus frequently undergoes division in 

 the cytoplasm of the egg. What is meant 

 by the fusion of the gametes? This is 

 always a fundamental problem. It may be 

 strictly a matter of the fusion of charac- 

 ters, or it may further be a stimulus to 

 embryonic growth. It is a remarkable 

 fact, however, that this stimulus to embry- 

 onic growth does not merely involve the 

 embryo itself. The limitations of the cor- 

 relations which seem to exist between the 

 mere process of fertilization and incitation 

 to growth in the extra-carpellary struc- 

 tures are extremely complex. On the other 

 hand, the process of fusion is often imme- 

 diately followed by the resting period. 



It would be extremely well if further 

 attention could be directed to the matter 

 of parthenogenesis in the higher plants. 

 Except in the ease of Nathanson's studies 



iipon Marsilia, little has been done to indi- 

 cate the conditions which may induce or 

 which may tend to induce this process. In 

 recent years, artificial fertilization, or stim- 

 ulus to a certain growth of the egg in the 

 lower animals, has been effected by chem- 

 ical agents, by changes in the density of the 

 solution, and by other means. This work 

 has demanded world-wide attention from 

 animal physiologists. It has been too much 

 neglected from a botanical point of view, 

 although the difficulties involved in similar 

 studies with plants would be, for the most 

 part, immeasurably greater. Yet it is cer- 

 tainly possible to prosecute such studies 

 along the lines indicated. 



Except in the ea.se of Sporodinia grandis, 

 and perhaps one or two other species of 

 Mucoraeese, mycologists have experienced 

 great difficulty in securing the zygosporic 

 stage of these fungi. The recent paper by 

 Blakeslee, announcing the conditions gov- 

 erning zygosporic formation in this family, 

 seems to open a field for investigation 

 wholly novel and suggestive. The sub- 

 .stance of his results is that this family 

 may be divided into two principal cate- 

 gories, designated, respectively, as homo- 

 thallic and hetereothallic, these terms cor- 

 responding to monoecious and dioecious 

 forms among higher plants. Sporodinia 

 grandis belongs to the homothallic type, 

 both gametes in every union developing 

 from the same thallus. Rliizopus nigri- 

 cans belongs to the second and larger class, 

 the hetereothallic type, in which the two 

 gametes are invariably the product of two 

 mycelia, which mycelia are sometimes of 

 diverse vigor. "When in culture, the tAvo 

 strains, as they are termed, grow together, 

 zygospores are abundantly produced along 

 the lines of contact. These are the striking 

 results of this important paper; but other 

 related physiological facts have been ob- 

 served, and only fiarther investigation can 



