GENERAL VIEW OF GREENHOUSE CULTURE OF HEMP PLANTS 

 Figure 19. Even at this early stage some of the plants have begun to flower, but none set 

 seed until a much later date. The female plants flower best at a temperature of 85° Fahrenheit, 

 while the male plants produce flowers at a much lower temperature, about 60°. It is not abso- 

 lutely necessary to have a greenhouse for experiments with hemp, as it grows well out of doors, 

 but it is possible to raise two generations a ^^ear in the greenhouse. 



attempting to establish homozygous 

 strains. It is, of course, impossible to 

 establish in hemp a pure line according 

 to the strict definition given by Johann- 

 sen. There is no reason, however, why 

 homozygous strains, similar to those 

 in Drosophila cannot be established 

 in the course of time. The long life- 

 cycle of hemp is a serious drawback 

 but this plant is no more undesirable 

 in this respect than Zea and Nicotiana 

 which have furnished the material for 

 investigations leading to some of our 

 most valuable genetic hypotheses. Since 

 hemp is adapted to greenhouse condi- 

 tions it has an advantage over corn, 

 and it might be possible to obtain two 

 generations a year by proper regulation 

 of food and temperature conditions. 



The staminate flowers occur in 

 axillary panicles as illustrated in Figure 

 18. Hemp compares very favorably 

 with corn in the quantity of pollen 

 produced. A slightly disturbed male 

 plant in full flower liberates a great 

 shower of pollen sufiicient to pollinate 

 many female plants. This charac- 

 teristic is of great value in hybridiza- 

 tion because the same male parent 

 can be used in a number of crosses. 



The pistillate flowers are borne in 

 short spikes, a single seed being pro- 

 duced by each flower. A cluster of 

 female flowers is illustrated in Figure 

 18. The female plants branch con- 



siderably (Fig. 17) when grown under 

 favorable environmental conditions and 

 will produce over 1,000 seeds. The 

 branching habit facilitates brother and 

 sister mating as well as varietal crossing 

 upon the same plant. The large num- 

 ber of seeds provides ample numbers 

 for testing different genetic ratios. In 

 order to hasten the production of 

 female flowers the temperature should 

 be kept around 85 degrees Fahrenheit. 

 Male flowers are produced at a much 

 lower temperature, averaging around 

 60 degrees Fahrenheit. At this tem- 

 perature the male plants continue to 

 flower for several months so that no 

 dilificulty is experienced in obtaining 

 male and female flowers at the same 

 time. 



One of the desiderata of ideal genetic 

 material is the facility with which one 

 may hybridize difi'erent strains. The 

 fruiting branch apparently does not 

 flourish when enclosed in tight paper 

 bags (Fig. 19) so it would appear that 

 a closely woven cloth tent is desirable 

 for this type of work. One meets a 

 handicap here in securing sufficient 

 funds for the purchase of such material. 

 I have already called attention to the 

 fact that hemp is a suitable greenhouse 

 plant and thus a genetic investigation 

 in hemp can be conducted both indoors 

 and in the field where climatic condi- 

 tions favor this procedure. In case 



