November ii, 1897] 



NATURE 



43 



placed in a poorly lighted room. Voung plants which had only 

 the round leaves, under these conditions continued to develop 

 only this form of leaf, while older plants which had both kinds 

 of leaves when the experiment was started, now developed on 

 the new growth of the shoot the round-leaved form . In the 

 case of plants on which the flower shoot had already developed, 

 side shoots with the round leaves were formed. 



Excluding the possibility of other conditions having an in- 

 fluence here, the changes in the form of the leaves have been 

 shown to be due to a varying intensity of light. The situation 

 of the plants in the open favour this view, since the leaves 

 near the ground in these places are not so well lighted as 

 the leaves higher up on the stem. In this case the eff^ect of 

 dampness is not taken into account by the experimenter, and 

 since dampness does have an influence on the size of the leaf, it 

 would seem that it might be at least one of the factors here. 

 An attempt was now made to prevent the development of the 

 round leaves on the young seedlings. For this purpose the 

 plants were kept under the influence of strong and continuous 

 lighting. The round leaves were nevertheless developed in the 

 early stage, an indication that this form of the leaf on the 

 seedling has become fixed and is hereditary. 



Hering found that enclosing the larger cotyledon of strepto- 

 carpus in a plaster cast so as to check the growth, the smaller 

 and usually fugacious one grew to the size of the large one, pro- 

 vided the experiment was started before the small one was too 

 old. Amputation of the large cotyledon gave the same 

 results. 



Other experimenters have directed their attention to the 

 eff"ect of light and gravity on the arrangement of the leaves on 

 the stem, as well as to the effect of light on the length of the 

 petiole and breadth of the lamina. Among these may be men- 

 tioned the work of Weisse, Rosen vinge, and others. 



Goebel has shown experimentally that dampness is also one 

 of the external influences which can change the character of 

 xerophyllous leaves. A New Zealand species of Veronica of 

 xerophyllous habit and scaly appressed leaves, in the seedling 

 stage has spreading leaves with a broad lamina. Older plants 

 can be forced into this condition in which the leaves are ex- 

 panded, by growing them in a moist vessel. Gain, Askehasy, 

 and others have shown that dampness or dryness has an im- 

 portant influence in determining the character of the leaves. 



The results of the experiments in showing the relation of the 

 leaf to the bud scales, Goebel regards as evidence that the 

 foliage leaf is the original form of the two, and that the bud 

 scale is a modification of it. 



Treub conducted some interesting experiments for the purpose 

 of determining the homology of the pappus of the Compositae. 



Gall-insects were employed to stimulate the pappus of 

 Hieraciic7n uvibellatum, and it was made to grow into a normal 

 calyx with five lobes. A recent letter from Prof. Treub states 

 that he later repeated these experiments with other species of 

 Compositse with like results, but the work was not published. 

 Kny found, in seedlings and cuttings which he experimented 

 with, that while there was still stored food available for the 

 roots and shoots, there was little if any dependence of one upon 

 the other. Hering comes to somewhat different conclusions as 

 a result of his experiments, finding that in some cases there was 

 a slight increase of growth, while in others growth of the one 

 was reciprocally retarded when either the other was checked in 

 development. Numerous cases of horticultural practice in pol- 

 lination of fruits shows that the form and size of the fruit, and 

 of the adjacent parts, as well as the longer or shorter period of 

 existence of the floral envelopes, can be influenced by 

 pollination. 



The investigations carried on by Klebs in the conjugation of 

 Spirogyra suggest how experimentation of this kind may be 

 utilised to determine questions which in special cases cannot be 

 arrived at easily by direct investigation. If threads of Spirogyra 

 varians which are ready for conjugation are brought into a 

 o'5 per cent, solution of agar-agar, in such a way that nearly 

 parallel threads lie at a varying distance in their windings, where 

 they are within certain limits, the conjugation tubes are de- 

 veloped and the zygospores are formed. But where the threads lie 

 at too great a distance for the influences to be exerted, the cells 

 remain sterile, and no conjugation tubes are developed. If now 

 these threads be brought into a nutrient solution, the cells which 

 were compelled to remain sterile grow and develop into new 

 threads, i.e. they take on the vegetative, though they are fully 

 prepared for the sexual function. Strasburger has pointed out 



that this may be taken as excluding the possibility of there being 

 a reducing division of the chromosomes during the maturing of 

 the sexual cells, a process which takes place in animals, and that 

 the behaviour of Spirogyra in this respect agrees with what is 

 known to take place in the higher plants, viz. that the reduction 

 process is not one which is concerned in the maturity of the 

 gametes. The same could be said of Polyphagus, in which 

 Nowakowski found that before the zygospore was completely 

 formed the protoplasm moved out and formed a new sporangium. 

 In Protosiphon botryoides Klebs was also able to compel the 

 parthenogenetic development of the motile gametes, and the 

 same thing was observed in the case of the gametes of Ulothrix. 

 If we are justified in interpreting this phenomenon as Stras- 

 burger suggests, the evidence which Raciborski gives as a 

 result of his experiments with Basidiobolus ranarum would sup- 

 port the idea that there is no reducing division in the chromo- 

 somes before the formation of the nuclei of the gametes. Raci- 

 borski found that the young zygospores of this species, in old 

 nutrient medium where the fusion of the plasma contents had 

 taken place, but before the nuclei had fused, if they were placed 

 in a fresh nutrient medium the fusion of the nuclei was pre- 

 vented, and vegetative growth took place, forming a hypha 

 which possessed two nuclei — the paternal one and the maternal 

 one. Raciborski interprets Eidam's study of the nuclear division 

 prior to the copulation of the gametes as showing that the 

 reducing division takes place here as in the maturation of the 

 sexual cells of animals, and looks upon the premature germina- 

 tion of the zygospore as showing that a paternal and maternal 

 nucleus possesses the full peculiarities of a normal vegetative 

 one. However, we are not justified in claiming a reducing 

 division for the nuclei preceding the formation of the gametes in 

 Basidiobolus from the work of Eidam, since he was not able to 

 obtain sufficiently clear figures of the division to determine defi- 

 nitely how many divisions took place, to say nothing of the lack 

 of definite information as to the number of chromosomes. Fair- 

 child has recently studied more carefully the nuclear division, 

 but, on account of the large number of the chromosomes, was 

 not able to determine whether a reduction takes place. He 

 points out, as others have done, the similarity in the process of 

 the formation of the conjugating cells of Basidiobolus and 

 Mougeotia among the Mesocarpe^, and to these there might be 

 added the case of Sirogonium, in which the paternal cell just 

 prior to copulation undergoes division. The division of the 

 copulation cells in Basidiobolus, Mougeotia, Sirogonium, &c., 

 suggest at least some sort of preparatory act ; but whether this 

 is for the purpose of a quantitative reduction of the kinoplasm, 

 as Strasburger thinks sometimes takes place, or is a real reduc- 

 tion in the number of the chromosomes, must be determined by 

 further study, so that the bearings of these experiments on the 

 question of a reducing division must for the time be held in 

 reserve. 



One of the very interesting fields for experimental investi- 

 gation is that upon the correlation processes which govern 

 morphology of the sporophylls (stamens and pistils) of the 

 Spermatophyta. One of the controlling influences seems to be 

 that of nutrition, and in this respect there is some comparison 

 to be made with the correlative processes which govern the 

 determination of sex in plants. Among the ferns and some 

 others of the Pteridophyta a number of experiments have been 

 carried on by PrantI, Bauke, Heim, Buchtien and others to 

 determine the conditions which influence the development of 

 antheridia and archegonia. PrantI found that on the prothallia 

 of the ferns grown in solutions lacking nitrogen there was no 

 meristem, and consequently no archegonia, while antheridia were 

 developed ; but if the prothallia were changed to solutions con- 

 taining nitrogen, meristem and archegonia were developed. All 

 the experiments agree in respect to nutrition; with scanty nutrition 

 antheridia only were developed, while with abundant nutriment 

 archegonia were also developed. Heim studied the influence 

 of light, and found that fern prothallia grow best with light of 

 20 to 25 per cent. Exclusion of the ultra-violet rays does not 

 affect the development of the sexual organs. He argues from 

 this that the ultra-violet rays are not concerned in the elabora- 

 tion of the material for flower production, as Sachs as suggested. 

 In yellow light the prothallia grew little in breadth ; they also 

 grew upward, so that few of the rhizoids could reach the 

 substratum. Antheridia were here very numerous. After seven 

 months these prothallia were changed to normal light, and in 

 four months afterwards archegonia were developed. 

 Among the algre Klebs has experimented especially with 



NO. 1463. VOL. 57] 



