344 METHODS IN PLANT HISTOLOGY 



acetic acid, 5 c.c. formalin, 100 c.c. 70 per cent alcohol). Figures like 

 that shown in Figure 120 are better in chromo-acetic-osmic acid. 



The period at which the various stages may be found varies with 

 the species, the locality, and the season. In Pinus laricio the mega- 

 spore mother-cells appear as soon as the young strobili break through 

 the bud scales. At Chicago, in the season of 1897, material collected 

 May 27 did not yet show archegonia; the ventral canal cell was cut 

 off about June 21 (see Fig. 120), the fusion of the egg and sperm nuclei 

 occurred about a week later, and stages like Figure 1192?, C, and D, 

 were common in material collected July 2. In the season 189G all the 

 stages appeared about 2 weeks earher. In Pinus sylvestris the stages 

 appeared a little earlier than in Pinus laricio. 



After the stage shown in Figure 119 A has appeared, it is necessary 

 to collect every day until the stage shown in Figure 119D is reached. 

 If collections are made at intervals of 3 or 4 days, the most interesting 

 stages, like the cutting off of the ventral canal cell, fertilization, and 

 the first divisions of the nucleus of the fertilized egg, may be missed 

 altogether. It should be mentioned that all the ovules of a cone will be 

 in very nearly the same stage of development; consequently, it is 

 worth while to keep the ovules from each cone separate. Stages like 

 that shown in Figure 120 are rare in miscellaneous collections, but if 

 ovules from each cone are kept separate and this figure is found, the 

 rest of the ovules from that cone will be likely to show some phase of 

 this interesting mitosis. 



Thuja and Juniperus are good types to illustrate the archegonium 

 complex and the large, highly organized sperms. In Thuja occidentalis, 

 in the Chicago region, a series from the appearance of archegonium 

 initials to young embryos may be collected between June 10 and June 

 20. In Juniperus virginiana, in the same locality, polHnation occurs 

 late in May and fertihzation takes place 12| months later. The mega- 

 spores are formed late in April, and the development of the female 

 gametophyte occupies about 6 weeks. 



The embryo.— The early stages of the sporophyte, usually desig- 

 nated as the proembryo, have been mentioned already. 



From the time when the suspensors begin to elongate up to the 

 appearance of cotyledons, instructive preparations can be made by 

 mounting the embryo whole. Dr. J. T. Buchholz has developed a 

 method for handhng these small objects. Remove the testa and then, 

 under water, hold the endosperm gently with forceps and press the 



